I think the cost-benefit differs. If the whole database is leaked, you just rotate everything. Only the stuff that has been used (which tipped you to it being leaked) has a real impact. Nobody's going to compromise every single account you have all at the same time, unless they're specifically targeting you, in which case they're going to get everything anyway. So on balance, it doesn't matter if some random malware gets 1 of your passwords or all of them. The real-world impact is about the same: limited. The cost of worrying about the extra security outweighs the benefit.

Another way to go would be tiers of password managers. Even if all of their unlocked integrity sucks, you can have one manager that keeps your most sensitive accounts, and another manager for the rest. You rarely unlock the sensitive one, and after you log in, you unlock it and exit it. Now you have much better opsec with very little additional cost.