Re: It's not "why", it's "how"
If you want to be picky people vote for a person, that person is (usually) a potential MP of a party, and the party that forms a working majority wins, usually with the same leader as entered the election.
It should be technically possible for MPs that won a majority of constituency vote to immediately switch affiliation, for the winning party to thus change, or even if it won for the PM to instantly change.
Hell, in the snowball chance in hell scenario, shouldn't it be possible for the PM to decide to quit as an MP, switch to an opposing party, have that gain a majority and continue on as the PM leading the opposing party..
Biting the hand that feeds IT
