Another important reason why crit fails on skill checks should not be a thing is that all checks in the game are necessarily universal - they're the same for every character, so the DCs must be universal DCs too.
Normally your DM tailors DCs relative to the person performing the action, and IF the result is that the individual simply cannot fail at all, then there is no roll (same goes for impossibilities too - if a task is impossible to fail or impossible to succeed, the DM narrates the outcome - for everything in between, you roll). With flat universal DCs however, those extreme no-roll situations are rarer because every possible character needs to be accounted for - so what might be a sure thing for one character is not for another, and we must roll regardless. This is why you cannot have critical failures on skill checks:
If a young child runs up to the party and says "My mum says Mystra is the goddess of the weave... What's the Weave?" There is no possibility that Gale will not have an answer to give - but it is possible that someone else might not know much about magic and may not be able to answer this (still unlikely but possible). Because at least one character might fail this check, the roll must be made regardless, but the Dc is low enough that most folks can't reasonably fail it - Gale certainly can't. With critical failures on skill checks, however, Gale CAN fail to answer this question, and that just doesn't compute.
