Why do bronze players constantly pick things they can't play?
Quite frustrating. Climbing back out of Bronze on a smurf account and just forgot how bad it is down here. One thing I notice a lot, between the constant use of the word "cancer," and intentional feeding, is that so many of them put so much stock into counterpicks and not what they can actually play. "Gnar is good against X so I should play Gnar even though I've only played him twice ever and he's a very high skill cap champion." This just results in them getting totally thrashed as they're clueless.
Bronze players, please, find something you're comfortable with. At this ELO, counterpicks aren't that huge of a deal. You can play just about anything and carry with enough knowledge of your champion and the game. You don't have to keep playing the highest skill cap champions because they're LCS picks or pick something you've never played just because some web site says it's a winning match up. Bronze Leblanc play for example is just laughable.
So again, please, find a champion to main for a role and stick with it. You'll get much farther by trying to master a champion than basing your picks off a misleading website. Is Kha'zix the best jungler? Not really. But you'll do much better playing him if you're comfortable than trying to first time Lee Sin.