None of the above reasons really!!! The main reason it was not as good as BB2 for me is the lack of any real genuine romance that people could be still interested in after the show was over.
Some of the BB3 characters might get it together but I think it would be more of a case of animal lust rather than human love.
Having said that I did enjoy the BB3 series. But there is no one that I am interested in after the event. It's left a vacuum where as BB2 didn't.