Maybe his men abandoned him like the others due to him being a crazy child burner? Although there's no real reason why they'd know or why they'd leave the island altogether rather than just renouncing him.
Abandoned their own homes? The Lannisters made no attempt to secure these fortifications? Why did the show bother...
Showing nothing? The writers are tired, bored, hate certain characters and favour others, probably all of the above
It would probably make more sense to show such a rebellion or a small garrison surrendering/fleeing in the face of an overwhelming force.
It would probably make a lot more sense to show Danaerys landing in Dorne or the Reach, those massive lands allied to her cause, closer to ships and full of grains and with no possible path of intercept or chance of disaster. Instead she chose to sail past the Stormlands which revealed she was invading Westeros to the Lannisters, before making a landing on Dragonstone which by all logic should not have been abandoned - to encamp her army of tens of thousands on an island which produces next to no grain.
It would have redeemed the show for me if Dany walked into abandoned dragonstone only to find it was abandoned for a reason, and one of Qyburn's birds drops a candle in the throne room at the last moment. It would make marginally more sense than the show as it is, where the characters favoured by D&D can do very stupid things and be rewarded for it immensely, which is a far cry from 1-3 wherein you do stupid things and you die. Reminds me when I played CK2 AGOT when I trapped an enemy army that outnumbered me 10 to 1 on the Stepstones, allowing them to starve to death having lost naval superiority. Dany just plopped her entire host on an island that could not support Stannis's far smaller army, when her enemy has the naval superiority apparently needed to just sail past Dragonstone whenever they feel like it
No signs of combat. Unlocked gates. Lots of dust. A dozen fucking dudes could defend the place well enough to give dragons some problems in plucking them out.
Remember, Dragonstone was built by Targaryens, for Targaryens. You can safely assume it's one of most dragon-proof places.
Besides Storm's End and the Dragon Pit in KL or Dragon Pit in Meereen it is the second most dragon-proof place in the world, I'd argue the second most dragon-proof if not the foremost (Storm's End may be stronker). The whole reason Stannis was there in the first place was to ensure the Targaeryans never came back, and eh, it's just demoralizing seeing how little effort is being put into the writing when even the smallest bit of consistency would go a long way
Also, IIRC, in the books Stannis orders to begin mining the dragonglass while he's still on the wall, but of course since show Stannis is retarded, and never added that the dragonglass kills White Walkers (the fuck was the scene with Sam for, then?) and having a fucking mine of it together, he obviously never orders that, so he apparently left the second most valuable position for him, both strategically and resource-wise, completly alone for Dany to capture (which probably removes possible book subplot - Dany captures Dragonstone and deliveries of dragonglass for Watch cease, at least until someone convinces her that Walkers are real and not just some bullshit a bastard of one of her parents murderers sells her to get away alive), so she might save the day and help Jon, so they can have hot secks on dragonback.
Seriously, the further it goes, the more inconsistent and dumb it gets. GEORGE YOU LAZY FUCK FINISH THE BOOK OR ELSE WE WILL HAVE TO DEAL WITH THOSE IDIOTS FINISHING IT. >:|
"I wish I'd read the books - I might have got a better idea of where it was all going," he said.
"I just felt as if I didn't get it, and had I read the books, I might have had a better idea of the role of the character - what he was meant to be. It might've helped."
"I could've done with another year," he said. "But as far as whether that character should've continued or not continued... or what the investment in him is, I really don't know."
And while he admitted to missing his old castmates - particularly Davos Seaworth actor Liam Cunningham - Dillane added that he otherwise was happy to leave Game of Thrones behind.
http://www.digitalspy.com/tv/game-of-thrones/news/a790111/game-of-thrones-star-stephen-dillane-doesnt-miss-playing-stannis/
This is probably the greatest reason for GOT's poor performance, D&D wanted to shift a plot-heavy show away from focusing on the writing (given how the plot gets increasingly tangled in plot spaghetti, so much so that GRRM almost certainly will never be able to tie all the plots off neatly), it can be understandable - focusing instead on the emotions of actors. So we get lots of economical shots of actors acting, which could work if the actors actually knew what their characters were feeling or were about. From what I've seen with Dilane, from last season's Sansas, Snows and Assassins all looking rather confused as to what they were trying to convey, from what I've seen with Dianna Rigg talking about how the show felt like it was produced by councils - D&D aren't directing their actors. From how they have completely misread characters like Oberyn... It's unlikely they themselves would know what to direct their actors with. Hence why Tyrion and Dany hook up extremely well despite not knowing each other, hence why time has been accelerating for multiple armies, characters, navies and kingdoms, or why characters have been able to ignore laws or strategic chokepoints that were major barriers in previous seasons (Moat Cailin and Dragonstone being the most recent and serious examples). None of it makes any logical sense and has no in-universe consistency with the previous seasons, so it breaks the show's verisimilitude, breaks the show's own rules in order to establish stories that are thematically appropriate for a good guys vs bad guys superhero story but stands out of character from the previous seasons.
Thus if you're just tuning into Season 7 having not watched the previous seasons, you see a story of good guys and bad guys reformed into good guys going up against clear bad guys. We left behind the S1 D&D where they said their motto was 'no good guys, no bad guys,' and now have our good guys vs bad guys superhero theme nailed down tight. Also lmao s7 they continue to shit on Stannis in how he destroyed the greyjoy fleet or siege of the islands or the whole dragonglass thing
Gil: What is it?
Sam: It's a map of Dragonstone. The Targaryens built their first stronghold there when they invaded Westeros.
Gil: That's dragonglass?
Sam: A mountain of it. Beneath the ground. Stannis told me, but I didn't think This is important.
Stannis: You don't look like a soldier. But I'm told you killed a white walker.
Sam: I did, Your Grace.
Stannis: How?
Sam: With a dagger made of dragonglass.
Stannis: Dragonglass?
Sam: What the maesters call obsidian.
Stannis: I know what it is. We have it in Dragonstone.
herpderp derp herpherp derp
George will finish the series
When the sun rises in the west and sets in the east. When Stephen King's bibliography runs dry and Cleganebowl memes blow in the wind like leaves. When Theon develops character again, and Littlefinger starts baneposting. Then he will finish, and not before.