Well if America voted based on being informed I think from political elections on down we'd see much different results.Reality TV show voting has always been, in every case, a popularity contest.
And I agree it wasn't fair to have only one hamster with a built in voting block going into the house.
Once they won a MVP her voters probably kept voting because the had evidence they could win. Just like the can't dance person on DWTS with the built in fan base stays on for way too long. They have people voting for non-dance reasons, and once they save them once, they feel empowered to prove they can do it again.
And it isn't like BB has to be fair, or has ever been fair, heck, even the regulators say it doesn't have to be.