Because realistically speaking, even people who do fine on the daily can have bad runs. And unless you are completely clueless in all things, you would be able to tell a good run from a bad one. Did you perform your opener correctly? Hitting your rotations as needed? Get hit by the things you could dodge? Subtle differences will show where you can improve your uptime and use what and when depending on the flow and mechanics, but you should already be able to identify any drastic difference in your own performance then and there. You don't need some deep introspective after the fact.

Unless you're taking it on yourself to upload your own performance, which some can't, then you're at the whims of others to do so; and not everyone else does it either. And you shouldn't have to be super paranoid about your parses; always asking someone to upload every run, just so some rando sees you're not actually shit, you just had a crappy day.