This addresses corrections like the blanket disclaimer added to p.5 of VOLO’S GUIDE.
If they added the disclaimer to indicate that the material in Volo's was biased, then why did they need to remove any of the information about monster cultures, backgrounds, or roleplaying? Just blame Volo.
We also removed a couple paragraphs suggesting that all mind flayers or all beholders (for instance) share a single, stock personality.
Instead of deleting the information entirely, what kept them from rewriting the paragraphs with that supposed suggestion? Just add more qualifiers to the paragraphs, clearly indicate this is only a starting point, and that your version of the monster can and should be whatever you want. Heck, don't the tables that follow (which are now all that remains for RP purposes) already pretty strongly hint at this customizability?
Side question: What if you don't want to roll up the personality of every single mind flayer or beholder you throw at your party, and were perfectly happy to use the "stock personality" for a random encounter or simple dungeon crawl? At least having a default gives folks something more interesting than "grr monster."
After all, the most memorable and interesting characters often explicitly subvert expectations and stereotypes.
As
@Scribe hinted at, this is a funny thing to say when the apparent goal is to remove expectations and stereotypes.
We didn’t alter the essential natures of these creatures or how they fit into our settings at all.
By his own words, they deleted the "stock personality" for each monster. Sure sounds like changing essential nature to me. If the removal really wasn't about essentialism, then why do it?