I'm virtually certain it's always been to evict.
I think it should change but it's the BB thing to do it this way. Don't think they will change, although if they ever would they do seem to be more peed of about it than usual.
But then again if they did the show would lose alot of it's point. The people leaving wouldn't actually be the most hated/wanted out but just the least liked. Hope you understand what I mean.
But then again, again (

) we are losing good HMs this way. Oh i don't know which way is best.