Does a crit on an attack automatically kill the attacked thing? Of course not, that would be absurd. Depending on the rules you’re using it either does max damage, or bonus damage. It also often is a successful hit even if the attacker would not successfully hit. It is the best outcome the attacker could hope to accomplish.
A crit success at a skill check is no different. You can not expect to convince the Dwarven kingdom that you, a human, are the long lost prince with a deception check any more than you can expect a first level rogue to sneak attack any noticable damage onto the Tarrasque. But you can score a hit, or convince them you believe you are the long lost prince and that maybe they need to find out why.
It sounds like what you think a crit anything is is pretty dumb. Success doesn’t begin and end at accomplishing the entirety of your goal with a thing. If it did we’re still going to have to make every combat crit a kill shot.
