Perhaps to you it is, but you have to remember Toady isn't making Dwarf Fortress for the sole purpose of catering to us players. While taking time to improve the short-term usability of his project would certainly boost the popularity of DF and the enjoyment of us fans, it would prove quite a large sidestep in an already humongous development timeline.
Or looking at it another way, figuring out what he did wrong the first time around, and learning coding practices that prevent those mistakes from happening again in the future, much less preventing the compounding of bugs when features rely upon existing features, would make the development time as a whole significantly faster. It would mean both a faster development time and a more interesting game. Plus, if Toady actually stops caring about fixing bugs so much that good numbers of people stop playing the game, it would impact donations pretty seriously.
There very much are still serious bugs created from the earliest days of DF that still cause massive problems with the game, including save corruption bugs even from fairly trivial things. The
adamantine spire bug was caused by the game never unloading data from abandoned worldgens or closed worlds, corrupting newly genned worlds with garbage data terrain if you didn't completely close out DF before genning a new world. That existed from the first version of DF ever made to the 34.x era, because Toady never tested that, and never went back to look at that.
What other code is causing bugs that have never been looked over?
Keep in mind, many bugs have existed since the game was in 2d. The reason we don't have more fluids than water and magma have a lot to do with the memory-saving map code from 2d days, and that's also why item data is saved in 16x16x1 lots, rather than something like 8x8x8. Many features may well
never get replaced, at least without player pressure to fix some major flaw. Presuming that any bugfix necessarily means stopping everything and working on nothing but bugfixing for years is a pointless false dichotomy when Toady has been on bugfix sprees multiple times in the past, and that has never forced him to choose between fixing everything right now and ever making progress with the game. And, I should point out, those bugfix sprees tended to come after a critical mass of complaints about how terribly buggy the game had become had bubbled up.
That paragraph was quite a bit of speculation into how Toady operates, and I can't claim to know him, but after experiencing the growth of this game (and reading those amazing dev journals!) I'd like to think it at least touches on some of the considerations he balances every day of development. I don't think anyone has the right to say exactly what he should or shouldn't be focusing on, no matter how large and amoeba-like the DF community becomes or how many players find themselves unable to enjoy the game in exactly the same way they've come to expect.
Yes, yes it does. Don't assume that this is a zero-sum game where any change in the way Toady works necessarily means things get worse. He isn't a soap bubble, he doesn't disappear forever if you poke him. He doesn't need a roving guard of rabid zealots ready to burn the heretics that question his ways. In fact, antagonizing others who have valid complaints to the point that it requires his attention as a moderator is one surefire way to drag Toady off of coding to handle user complaints, which is something he very much has had to do in the past, and doesn't like doing.