The rules are finally "good enough and simple enough" IMHO. They support the goals of a successful D&D game which is everyone having fun participating in a fantasy adventure without having to be an expert, which is why the player base is exploding and pulling in people who aren't particularly nerdy but love the escapist fun that a TTRPG can provide.
I know I certainly enjoy getting away from my computer and sitting around a table with real people and telling wild stories

(not to take anything away from those who play via computer, of course, but I don't think that's the majority?).
To majorly mess with this success, just to "refresh" the ruleset, would be a big mistake IMHO. There's a
gritty crunchy option available to those who want it (in PathFinder 2, or other RPGs). D&D needs to keep its grip on being the most popular RPG, and that means a stable rules base that people can become familiar with (and eventually expert).
The way to keep things fresh (IMHO) is to, slowly, expand the available classes, introduce new spells & monsters and settings to go with them. And of course adventures.
And finally a book they should absolutely produce is a more friendly guide to DMing. The DMG is terrible for new DMs, IMHO, and D&D needs more and more DMs. "How to become a great DM" or some such.
(Edited before someone flags "gritty" here too!)