"At no point was there a situation where the general populace had the opportunity to vote in a conservative government with a leader who had campaigned for the party, leading up to an election."
No, no one has that direct option, but at any time the Maidenhead voters could have opted to to have a different representative. We, the public, don't elect leaders directly in our system; we elect representatives and they chose between them who should lead and thus be eligible for consideration as PM.