Here's the 5e release rate of crunch books beyond the core 3.
2015: Nothing
2016: Volo's Guide to Monsters
2017: Xanathar's Guide to Everything
2018: Mordenkainen's Tome of Foes
2019: Nothing
2020: Tasha's Cauldron of Everything
2021: Fizban's Treasury of Dragons(I forgot about this one)
2022: A book of mostly reprinted stuff with slight changes: Mordenkainen Presents: Monsters of the Multiverse
2023: Bigby Presents: Glory of the Giants.
So less than 1 per year, but not 1 per 2 years. Still glacially slooow.
Edit: And there are still only two really solid crunch books. Xanathar's and Tasha's where it's not a bunch of monsters and lore mixed in with a little crunch.
But, again, you're telling me what's in it for you. Fair enough. But, you're still not telling me what's in it for WotC or the rest of us. I can barely keep up with the amount of crunch for players in 5e as it is. I'll freely admit that. And, watching a new player, which my group has just gotten absolutely struggle with all the options that already exist for 5e tells me that there is not a whole lot of need for more.
Again, this idea of a need for a constant stream of crunch. Why? Most of it was never used by a given group. Think about your 3e or 4e games (whichever you played lots of). Did you actually use more than a tiny fraction of the material available? We certainly didn't. Thousands of feats, spells, book after book of magic items and equipment. All for what? So it could sit on the shelf and gather dust?
No thank you. I mean, good grief, by your own count, you've gotten a crunch book every year with a couple of exceptions. I highly doubt you've put much of a dent in any of it. How many FIrbolg characters have you seen in your games? How many aarocockra? I've just seen my first Samurai fighter in my current game. Fizban's saw a gem dragonborn and a couple of spells. 200 (300?, no idea) pages of material and it could have been three pages max as far as my table is concerned. Volo's hasn't even had the cover cracked in my games AFAIK.
A book a year of crunch with 2 exceptions and this is "slow"? Never minding that many of the modules come with crunch as well. And SCAG came out in 2015, which had crunch.
It's only slow in comparison to 3e and 4e. Fair enough. But, we know that 3e and 4e were mistakes. They were very, very big mistakes. I like the fact that the hobby is growing year on year. So, how is it good for the hobby to increase the rate of crunch books? Will having fifteen more classes attract new players? Are there people out there who are saying, "Well, I'd play that new D&D thing, but, y'know, they just don't have a Warden class"?
If I had my way, they'd go back to 3 books a year with a 4th as a sort of possibility. 2-3 adventures a year and a supplementary book of some flavor. That's the pace I want.