Chose my best champ, teammate banned it, can't carry the team after they lost their lanes.
Since it is almost pointless, might as well removes it to give less false impression?
It's not to prevent bans, its to help organize a team comp. It's a dick move to ban what someone is hovering, and from I've seen it's usually an accident when it happens, otherwise it's to ban a pick/ban champ when the person hovering is towards the end of the draft. I can probably count on one hand the number of times I've seen it done intentionally just to troll.
Because if you aint first pick, then the other team will have a chance to get it as well.
lemme tell you a story, zoe is released, zoe is op, sees teamate is 3rd pick (so i pick, then 2 enemies, then him and a teamate), i ban zoe even tho he wanted zoe, turns out, he wouldnt have gotten zoe, sometimes you know, sometimes you dont want to ruin your last cherished thought of rito knowing their shit and you perma ban irelia every game no matter what, who knows
To premtivly help identify who to mute
To passively encourage players to chat with each other even less.
Even an ARAM only player like me can see the purpose, so you can see it too. The bad side is that sometimes a troll does ban your hovered over champion, but I bet it is more common for a team mate to ban it because the enemy team would get the champion instead of you if he isn't banned.
As a totally unrelated fact; Whining isn't manly.
Declaring your champ is supposed to help build a decent team comp. You are however not 
teed that champion, as at any time your team and the enemy team could ban it.
Everyone gets a ban and they can ban whoever they’d like without repercussion.
