Sure, I get that there are people who find value in this stuff, and I am not trying to bash those who do.
Here's the thing though - I don't need a book of plot hooks. I don't need a bunch of deep lore that may or may not work with my campaign. I don't need droll Elminster anecdotes. I just need some damn monsters.
Earlier editions understood that there were different markets for different products. They had rules-heavy monster books and more lore oriented stuff like Monstrous Arcana and Elminster's Ecologies. By contrast 5E has ... $12.50 worth of monsters packaged with $37.50 of stuff that I couldn't care less about.
Here's my thing:
How many unique monster stat blocks did you use last session?
Last session of D&D I played, it was
one. Rocs.
I've seen more - sometimes maybe 5-7, if we're having a very diverse kind of night.
D&D's been out for 2 years now. If I ran a session every week and used, say, three distinct stat blocks every week on average, no repeats, no homebrews, no templates, not counting racial modifiers (so "dwarf scout" = "orc scout"), I've used 312 monster stat blocks.
That's not even every monster in the monster manual. And it's not counting running the official adventures and using their stat blocks (which, by far, has been my personal experience - I'd be surprised if I've used
half the monsters from the MM).
I might be atypical...but how many monsters from the MM have you used? Like, do you have a %? A weekly average? Is it especially high?
If so,
Here's 250 more. And
here's 400+.
Here's a load more, on the cheap.
How long do you think those would last you? Because me, I could play with these stat blocks for
decades and not use them all.
5e's got more of a glut of monster stat blocks than it does any other product. There are perfectly good monsters in these products that I will just
never use. Hell, that last session of D&D? It's the first time in
ever that some of the table fought against Rocs! These guys have been playing for 20-30 years!
What I've got less of is inspiration, setting material, useful plot threads. Context. My campaign doesn't need to be set up to accommodate them already, they
inspire me to use them in my campaign. I didn't know I'd have ceremorphs in my game until I really liked the idea of making one an antagonist!
I don't need 1,000 stat blocks (though I've got 'em!).
I need maybe 5-10 stat blocks and 100 awesome ways I could use them.
"More Stat Blocks" is a solution to the problem of "I don't have enough monsters!"
I don't fully understand why someone would have that problem at this point in time in 5e, unless they're running a really unusual group for one reason or another ("Oh, I can't use undead or humanoids or beasts, so once you remove those...." / "Oh, I'm philosophically opposed to non-WotC stuff" / "Oh, my games feature 30 monsters every night and we meet 3 times per week, so I run through these books in like, three months")
My problem is more, "Why should I use Mind Flayers when I've got 1,000 stat blocks to choose from?"
That one page gave me at least a small handful of reasons to do that.