How does baseline Risk sell copies every single year without changing the rules? Or Catan? Or any other evergreen game?
If we've actually moved into a world where D&D has become a real mass market game rather than the purview of a small number of hobbyists who need to be milked for their cash like cows every 10 years, that would actually be a good thing IMO. The game shouldn't be changing so much that they have to force players to buy new rules every decade to "stay current" to turn a profit on the game. If they're able to reach a point where they can get a consistent profit from new players aging into the game combined with people having to replace books periodically, then that's actually an astonishingly good thing for D&D as a game and for Wizards as a company. Even if there are a lot of folks who wish that D&D had settled into being that kind of game at some different point in its development history.
If the game ever hits that point - whether its now or in the future - then I could see a cycle where every decade or so a revised rulebook is published to gather together errata, cleaner explanations of existing rules, and any new rules that have been published in the interim. That's basically how Call of Cthulhu works for example and it's on its 7th edition. D&D is in a weird state where everyone expects edition changes to be huge changes to the game because of how 3rd edition brought 20+ years of game development advances into the game all at once, but it doesn't actually have to be that way.
Also - and I think this gets underestimated - tying themselves to DDB means that any major changes to the game have to be supported by DDB or else they lose all of that work the same way they basically threw away all of the 4e tools when 5e came out. When they bought DDB that was another mark to me that they were planning on the core of the game being pretty stable long term because if they were thinking about making big changes, the DDB purchase would have been a bad move on their part.
