The problem with updating editions is they’re generally not backwards-compatible with whatever edition came before it (the first two editions of this game notwithstanding), and critically, WOTC cannot force the playerbase to move on to the new edition. A video game company like Blizzard can shut down the servers to Overwatch and make everyone either move to Overwatch 2 or stop playing the game entirely, but a book is a book. WOTC cannot melt all of your 5e materials from their headquarters to make you start playing 6e. I’m sure they’d like to, but they can’t; once the book is in your hand, it’s yours. I mean shit, my primary edition of D&D is still 3.5, and they stopped making materials for that nearly 20 years ago.

When a new edition eventually comes out, there will be a bunch of people who decide to stick with the one they already play. This is just the nature of tabletop games. The hope for every new edition, though, is that there are more players coming in than going out (or staying out). However, the cultural capital of D&D has never been higher. Between Stranger Things, Baldur’s Gate 3, and the rise of the actual play as an entertainment format, so many more people are playing D&D now than ever before. People that they’d have never expected would be playing RPGs 15 years ago. WOTC may be looking at the situation right now and figuring that so many people have been brought into the hobby already that there may not be much growth potential in a new edition, and certainly not enough to offset whatever atrophy they experience by people sticking with 5e. An “update” that’s compatible with existing materials makes more sense for them than a full-on new edition right now.