The next rules update will be in 2028, 5.5 is just a money grab to hold them over until they need to make serious changes in the face of rising competitors.
I think the old editions were the money grabs. Whenever sales flagged on an edition, TSR/WotC introduced a new one to temporally juice sales. Each new edition had swiftly diminishing returns, and also split the player base. And created opportunities for competitors to jump into that divide (c.f. Pathfinder).
The experiment of 2024 is to NOT go for the short term money grab, but to stick with what has been working and try to maintain a steady player base. I'm sure they are expecting a spike in sales from the new books with some new rules and a lot of new art, etc., but the priority is to keep the ball rolling on what 5e has already built.
This is not me speculating. WotC has been very up front about the new business plan. It makes sense. It's how most companies operate, relying on sustained growth rather than an unpredictable boom/bust cycle.
WotC keeps telling us what they plan to do, but since OneD&D was announced, I feel like most folks aren't listening:
1. They don't like the old editions paradigm because it was bad for the brand and the company, sacrificing long term stability for short term profits.
2. They are therefore rejecting it, and they are adopting evergreen rules with room for gradual evolution as the new paradigm for D&D. 5e has been incredibly successful, so that is D&D going forward for the foreseeable future.
3. They will use digital tools, specifically DnDBeyond and the Virtual Tabletop currently in development, to enhance growth by building on and better monetizing the existing strong player base.
WotC specifically doesn't want you to feel like you HAVE to replace all your current 5e stuff as soon as the 2024 books drop, because that just incentivizes a lot of folks to break away and stick with their sunk cost. Instead, they are offering shiny new books that will tempt you to replace the core three, but are endlessly emphasizing that you aren't required to swap, and if you do so, you don't need to replace all the rest of your stuff. This seems like a much smarter approach than, "New edition time! All your old stuff is now junk, suckers! Hey, where are you going?"