I thought you said they weren't really in it for anything more than shoot and be shot?
I said I'm ok with it in moderation. It's a theme and a thing to do in games. It isn't *the* thing to do. A man's got dreams, after all.
They don't seem like 'veterans' in that sense, at least.
20+ years roleplaying has kind of made people sedentary in their ways. We've all played high concept, high roleplaying games. Eventually the group always came back to, ya know, yolo swag as the easiest and most readily enjoyable kind of roleplaying. This group is the comfort zone of roleplaying for them, but it means they've developed a way of playing games that many GMs find frustrating.
And while railroading is hated by the players, you gotta do what you gotta do to make your game work, and be fun for you to run as well as for them to play.
I get a lot of advice from one player in particular. Or if less advice, more statements about what they do and don't find fun. The kind of person that when I described the scale and scope of RT went "I think the scale or the scope isn't fun. I'd rather be one ship with 20 guys swashbuckling in space. Having a fleet is boring. Having an empire is boring. Building an empire is boring. Gearing up over time is boring. Having thousands of guys at our beck and call is clunky and boring because commanding people to do things isn't fun." That's generally what I have framing my decisions about game, is at least one person constantly undercutting the setting. (He is, in fact, just as steeped in 40k lore as I am. He's way more selective about what he likes. It should surprise no one he's playing the Eldar.)
Like, really, it almost sounds like you've been resentful of them, apologies or no.
As a group we have a lot of history but some (from my point of view) restrictive ways of playing and handling games has become cemented with them. And some interesting social dynamics have formed in the group if you're sensitive to those kinds of things.
So if I sound resentful, it's because I've watched several GMs walk away from games they were trying to run for this group because some of the players just refuse to stop being "themselves." Laughing at, straight up ignoring or executing NPCs on a whim like they're playing a video game, stupid non-RP character names (I wouldn't let one player name his character Duke Dickmissile in Dark Heresy, so he went with Govelious Pwnus or something), intentionally lazy character ideas ("I fly a ship and I have a gun" was literally one player's entire character concept), interrupting a GM in mid-sentence description or talking with "Yeah, whatever, I shoot him." Other players have played and then left because the clique doesn't know how to play any other way anymore. They've written off serious roleplaying entirely. So, while you get moments where they're engaged and you get some real RP, most of the time you're fighting against their tendency to just kind of be dicks, to the setting and in some cases to the GM. It's like at their worst, they sense the investment and effort someone has put in and their first instinct is to start trolling. Unless you're literally there to just facilitate their fantasy, you end up in an adversarial position of trying to defend your game.
I have 4 other players besides the old guard, and even between all of them, they can't really tilt things any other direction. There are several newbies and so they just kind of get swept up in the wave. But I have two other long time roleplayers who, even despite wanting to try something different, can't really ever seem to overcome the inertia. Case in point: everyone did want to know what the AI was all about, but the Captain completely closed that avenue when he opened fire instead.
Basically, to the clique, 40k is played like its a Flashgitz video sometimes. Which is funny and all that shit. But it gets old. It gets old when you put the time in and you're tired of playing the same kind of game over and over, which eventually turns into one long running joke doing laps in the meme center. And it's frustrating when you're the GM and you feel like you yourself are getting pulled into the same orbit.
Trust your players to be able to handle the occasional risky plot or two.
I'm a pretty firm believer that adventures have to have pay offs, and you don't just construct death traps for your players. Misery isn't a good motivator for a lot of people, and the game isn't Call of Cthulhu despite all the insanity and corruption and stuff. So I trust them to handle risky plots. I don't want to get into revengeance GMing though. That's what I'm cautioning myself against. The best revengeance you can have as a GM is an encounter you put next to no effort into and the players thought you designed it to kill them and took it completely seriously.
Put another way, wanting to put the fear of god into your players as a goal isn't a good place to GM from. It's been tried with this group before and they've just been around too long, played under too many GMs, seen too many GM tricks and are too willing to say "meh fuck it I don't care" when they've been put in a corner. So I'm trying instead to focus on doing something that actually reaches them in a way that they don't have to be brats to stay entertained. Be that a satisfying combat, an enemy set up for them to knock down or an actual original idea that took root. Because the truth is when you've been playing with the same group for so long, if the GM isn't delivering fun to you, you either start making your own or you stop showing up to table. I'm still currently taking it as a challenge to bust through the jaded gamer mentality and try and spark some genuine interest and novelty.
What's really frustrating is that I've seen good roleplaying out of these guys in the years past, but the older they get, the younger they seem to act at table. Or as one player puts it "I live an adult life and deal with depressing adult shit all day. Game is where I come to unwind and get away from all that." That attitude reflects a lot of their reactions to just about everything in game.