Why do the last players get the bans?

I know that before picking later was mostly considered worse since you wouldn't get as much of role selection. But now that's irrelevant since the roles are already chosen for you. Yeah you can trade, but even that doesn't seem to be impacted much by the pick order. It just feels like picking later is almost entirely better since you're less likely to get countered and can pick something better with what other players picked. So it feels to me like the first 3 players on the team should be the ones to get bans.

Alternatively, there doesn't really seem like there's any good reason why not to just give every player a ban, but I think that's generally agreed upon already.