I wish you and others would stop doing this. The majority of creatures in a game world are humanoid. Just cause the MM has a large variety of non-humanoid creatures, does not mean you will encounter a large number of them.
How many Otyugh is your character ever going to see? Treants? Xorn? Darkmantle? Grey ooze?
Now how many humans, dwarves, elves, gnomes, orcs, bugbears, drow, gith, gnoll, lizardfolk, kobold . . . . Do I really need to continue? Not only are there more humanoid creatures in the MM than you give credit, but by sheer numbers a player will encounter, the ratio is probably 100:1.
I wish people would read all of the words I write and not just some of them. I also wrote "Casting it on a mook (not every weak foe has the word mook printed on his forehead) is pretty much a waste." and "If the PCs are in town with a lot of humanoids, this spell might have some limited traction. If not, it's probably a waste of a prep."
We were just in a "dungeon". There were human guards outside. We had time to prep. If I had the spell, I could have prepped it. We had the four outer guards, a room of a dozen human guards, two higher level humanoids, 5 lizard-like humanoids and about four kobolds. We also had a dozen and a half undead, a half dozen other beasts, a dozen flying beasts, one major (big) monster. Now, I am being a bit vague here due to spoilers.
Out of all of these creatures, only 2 are worth casting a Hold Person on. Two humanoids worth it out of about 60 creatures. In a dungeon where we knew there would be some humanoids. The vast majority of the rest of the humanoids went down in one or two swings. Those foes are not worth wasting a Hold Person on.
So yes, there are tons of humanoids out in campaign worlds. There are only a tiny handful worth using a Hold Person on.
Also, there are not "more humanoid creatures in the MM than I give credit". Out of the 40 "As" in the index, 4 of them are humanoid. And many of the humanoids from the MM (21 total) are from Appendix B, the NPCs (i.e. not races, but classes/professions). I checked this out some time back. I don't remember the exact percentage, but it was something like 10% or 15%. If you claim otherwise, please go count it yourself.
So although your opinion is noted, it doesn't invalidate what I wrote.