Well, honestly, the last scandal seems to be just the straw that broke the camel's back. Last month Johnson - barely - survived a vote of no confidence over the lack of trust people had in him and how Government wasn't trustworthy anymore etc.
Earlier, he appointed Chris Pincher as deputy chief whip. Fair enough. But Pincher had a bunch of scandals swirling around him - several allegations of sexual misconduct and inappropriately touching.
Now, when this surfaced, Johnson claimed - and had others claim in name of the government - that he didn't know anything about them. Then that he know about unsubstantiated rumors but nothing more. Then, that he know about official charges, but that they'd all been dismissed. Then, that he knew about them, and hadn't all been dismissed but that they weren't serious.
He made - yet another - stupid mistake in appointing someone with sexual misconduct charges, simply because he's loyal. Because personal loyalty is such a good basis for government. Now, he's done that kind of thing before and has gotten away with it. But this time around, apparently, he lied directly to his ministers and chancellors etc, so that they'd go on TV and spread his lies. Then, when the truth came out, all of them looked like they'd been lying and protecting the PM. And, again apparently, this sort of thing has also happened before. They're all tired and sick of being dragged down and being either lied to, or asked to lie, because a government that isn't trusted and doesn't have support, simply can't govern.
I'm definitely not saying I like the Tories. Some of them are horrible human beings with revolting political ideas. But, at least when compared to US Republicans, they have some amount of pride and shame left, and actually use it.