A white room battlefield strewn with blood today.
I'm sure there are players that are amenable to spending a fair number of combats as a menagerie of critters. But they are not generally the type of people who have carefully crafted and optimized character builds (and when they are those people they are already playing a Moon Druid), as any optimized character is going to be mostly better than a comparable CR beast, and certainly more versatile, and this is when they are at a level where there is a suitable CR beast to make full use of the level. Even in a scenario where the critter is objectively better most people have shown up to play a particular character in whom they are invested, not whatever Mr. Cool Sorcerer wants them to be to prove how overwhelmingly powerful he can be when he novas his resources. And, as a practical matter the polymorph friendly players have to be players who do have sufficient system mastery to play whatever statblock they are handed on the fly, so that rules out a lot of the people who don't really care one way or another.
Anyone can appreciate it as a novelty, and once they've used up their own resources in HP, abilities, spells, etc. getting handed a fresh stat block starts looking pretty great. Also cool when you've grown bored with how your character fights or when your normal tactics have been frustrated by the circumstances. So if I'm a Rogue and there is a consistant source of disadvantage blocking any possibility of sneak attack then by all means turn me into something else. If I'm a non-Martial Bard whose out of both spell slots and inspiration with my only remaining utility being to Viciously Mock the enemy then by all means change me (after I've gotten a good insult in). And if I'm almost dead as anything then sure, I'd rather be a fully alive giant ape than making death saving throws. But I think double T-Rextasy working out both mechanically and for table dynamics is pretty situational. I also suspect the party that starts every battle double beasting it is going to start running into fewer encounters where that is viable real quick unless they have a DM fully committed to following something prewritten. I also suspect the sort of Sorcerer who quickens every attack spell so he can debuff with a cantrip first, and throws metamagic dogs at enemies all day long, which is what this thread started out about, is usually not going to have the resources left for twin polymorphing by time other people are depleted enough to want it.