This is a highly disreputable way to pick a prime minister. I know it's not the first time and that it's not just Tories who do it. I think that a general election should have automatically been triggered.

Be careful what you wish for. If that had been the case, and if the Conservatives were likely to lose many seats in a General Election, then sitting members would have been less likely to come-out against Boris, and he would still be PM.
The current party can only work within the parliamentary party rules as they currently stand.
Labour could call for a vote of confidence on the current government, but chose not to.