Hook Horrors aren't that interesting. They're bipedal crabs that leap from the ceiling in the Underdark.
I agreed with the rest of your post, so didn't quote it.
I disagree with this. I was a biology minor in college just because I found it so interesting. I don't think that I have a unique interest in the "neat things about animals" so long as we focus on mainly the neat parts rather than a full writeup of every little thing. I probably care more about the mundane, but if you read any Cracked.com article about animals, one can see the interesting appeal of lots of animals, and just how crazy they can be.
E.G. Foxes. I don't want to read a whole long thing about the mating habits, diet, etc etc etc of foxes, and then read the same thing about stoats, or ermine, or mink, or weasels, or fishercats etc. However, the mother fox being willing to attack something the size of a bear to defend her young IS something that I'd include in the entry.
But conversely, I do want to know the mating habits and diet of the fox, as it's relevant to the ecology. I just don't want to read the same basic thing over and over, nor do I want to take up a ton of the entry to say such things.
I think every animal has something pretty interesting about it (and so should every monster). Heck, I think "A modestly intelligent group of opportunistic hunters who will callously add intelligent prey to their larder, so long as it helps, rather than endangers, their tribe of alien-thinking cockroach beings." Is a pretty interesting monster, myself, YMMV.
I wonder if a solution to some of this, similar to the statblock categories in third edition, might be an ecology index? In science it's done all the time: e.g. carnivore vs. omnivore vs. herbivore. I'm referring here to the categories or types in 3e of, for instance,"incorporeal" where all of the properties of "incorporeal" were listed at the back of the book.
In play I found this cumbersome in some cases, because if I didn't have it memorized I needed to look at the back of the book for the 50% miss chance or whatever. But that was usually in on the fly combat.
However, since the ecology of the monster could be important in some instances and entirely irrelevant in others (random encounters or somesuch), I wonder if this would be less cumbersome for an "ecology index" rather than a "combat relevant stats by type" index?
I'd have to go through dozens of entries to see exactly what would go "in the back" as opposed to "in the entry", but I certainly think that anything mundane and repetitive could go in the back with a simple category or descriptor like "carnivore" "insectoid" "arboreal" "amphibious" "monogamous" etc as a way to look up further details.
Maybe hook horrors would fall under "insectiod" (which might include appearance and diet, perhaps even mating and their clutch of eggs), "familial" (which would mean that they care for one another and their children rather than a "to each his own" style), polygamous (not taking a single mate), and group hunters (3-10) (this would fall under the old "number encountered" section of monster manuals going back at least as far as AD&D).
So from the keywords/phrase/classification of "insectoid, familial, polygamous, group hunters (3-10)" we'd know almost their entire ecology. Any additional interesting facts or contradictions could then be added within the specific entry. e.g. if they had all of insectiod except that insectoids normally are solely carnivorous in the index entry and hook horrors are omnivorous we'd have: "insectoid (but omnivorous, preferring meat), familial, polygamous, group hunters (3-10)".
All of that said, I'd still want to be able to read the ecology as interesting society and ability tidbits, written as descriptive text rather than as it's own statblock. While I think using classification as a tool would be an excellent way to dodge writing the same thing over and over, I'd hate to see it become an "ecology statblock" of keywords that again cause the creature to be treated as a (ecology) statblock rather than as a being.