The cabinet were fed up with being sent out in front of the media to say stuff that later turned out to be untrue (and known to be untrue at the time they were sent out there). They'd lost all confidence in the PM and the number 10 operation. If you fundamentally doubt any reassurances you are given by your boss, then that makes your job impossible. Whether or not a lot of gullible people liked Johnson's airy, flippant, entitled manner is irrelevant. Being a 'right laugh' in the opinion of some of the electorate, doesn't mean you're capable of leading a major operation, responsible for governing the country. They did entirely the right thing getting rid of man baby Johnson, regardless of what happens at the next election. The shameful part is that it took them quite so long.