If BJP had given support, outside for Mayawati to form a government then most of these people that strayed, and most of these people that voted for congress would have gone to vote against. It is the total destruction of an alternative government that lead to this problem by BJP, as most MP's are very afraid of facing elction exxcpt opposition.
BJP is at fault because it gave no alternative to UPA. Further even if governmnt fails, there will be a caretaker government meaning the failed government will be still running. Therefor it was very ncesssary for an Alternativ government that would have stop all failed policy. In fact BJP helped Congress win the trust vote, Further maybe all parties are in the hands of congress.
