"There's no common sense in that."
There are plenty of reasons to do it.
Sometimes it's a high priority champion and you/your team don't have first pick.
I am always willing to grab a teammate's champion for them if I can, but there are too many times I've given people the benefit of the doubt and the enemy team first pick locks in whatever OP shit I was going to ban.
Drafting is a part of the game.
The only reason you should have a set champion you want to play is if:
A. The champion is stupid OP and a priority pick.
B. You're a OTP.
Otherwise you should really be drafting around making a good comp and choosing to counter the enemy lane/team.
Don't be surprised if you're playing for condition A and your champ gets banned. And if it's condition B, just be a good sport and dodge when your one-trick is banned, just because you "can play more than 1 champ" doesn't mean you can play them well, and you're only hindering your team and messing up your own MMR at that point. MMR is way more important to climbing than the 3 LP you'll lose.
claiming there's no reason to ban a champion hovered by a teammate is just naive and self-centered since this is obviously something that happened to you personally that you are upset about.