The EN World kitten
I suspect that there are several answers to this, one of which is that some people have largely lost hope for more things related to world-building and "simulationism" (to use a loaded term) given how much WotC has moved away from these things over the last several years. Personally, I think that's a shame, because I still recall how much things like Aurora's Whole Realms Catalogue (affiliate link) helped to flesh out worldbuilding and make a campaign setting feel more alive. When most "settings" are little more than a single location, maybe with a bit of background and some new monsters, you start to lose hope that you'll ever see more.1) So why aren't you arguing that linguistics, coinage, taxation, conscription, etc., be put into the official games?
Another reason, I think, is that a lot of players (especially newer/younger players whom a lot of people keep touting are being brought into the game) don't really have any conception of how useful these things can be. I see a lot of players who come into D&D from things like Skyrim or Final Fantasy, where the "world-building" that isn't directly relevant to the plot of the adventure gets put into what I call "packets" (i.e. textual findings which you can stop and read, and which seem to be presented in a way that distracts from game-play rather than adds to it). To that end, they tend to disregard "window dressing" as taking away from the exploits of the PCs.
While I can understand that view, I find it limiting; you can make the world engaging by fleshing it out more, and a lot rests on how official material makes it clear that these things enhance a game, rather than being distractions. (This is much in keeping with the loss of D&D's endgame, where domain rulership is the natural extension of dungeon-raiding and clearing a dangerous wilderness. The game did a bad job explaining how this was a shift to a new type of adventuring, rather than an end to it, and there's a similar problem with other aspects of fleshing out a game world.)
It's not. This viewpoint, as I see it, is an issue of how to turn "extraneous" material into more than just flavor text which the players' eyes glaze over at. While I won't go so far as to call this a "problem" unto itself, simply because this lends itself more to certain play-styles than others, and certain people prefer certain play-styles, I think it's hard to deny that certain modes of play are being starved for options in terms of the official materials, and this falls under that category. In that regard, while there are certainly people who don't care for much beyond their own character's exploits, I suspect that there are a lot of players who'd be quite happy to engage with a much more dynamic, detailed world. It's no coincidence (I think) that the Forgotten Realms was the single most fleshed-out campaign setting TSR produced, and is now the flagship setting for D&D.2) Most people, AFAICT, consider linguistics, etc., to be either cool but unnecessary for the actual game, or just more info that will never be actually used in the game and will likely bore the players if it is used. Why is slavery, rape, et al different?