The problem is, you're conflating "shiny new interface" with "an interface that actually performs a vital mechanical task of providing the player with information they need to make decisions".
Once again, there are tons of low-hanging fruit like sortable lists that won't need significant changes over the life of the game, because we won't ever need to stop sorting the lists. It also doesn't take much time to create sortable lists or, for that matter, introduce the mechanics to make such sortable-lists easily extensible with essentially no effort on the part of Toady.
In fact, the same exact argument can be made against things being put into the raws - and yet Toady does take the time to put things into the raws, even though such code is much more likely to eventually be overwritten than interface code.
You can, in fact, also say the same thing about bugs - why fix bugs, when you'll just create more bugs later? Other than, you know, compounding bugs on bugs makes previous bugs much more costly to fix, and makes them significantly harder to isolate in the first place. If Toady doesn't think about how the interface works, he will get less and less able to ever fix its problems.
You're throwing out an abstract fear of needing to make everything perfect at all times as a reason to never do anything to alleviate the serious problems at hand - it's like saying that there's no reason to ever take a shower because you'll just get dirty again, later. And what the current interface has doesn't just smell, it's getting to be an infection that is plaguing many aspects of the game.