It’s particularly galling when the prime minister introduces very strict regulations, that even the queen has to abide by (infamously mourning for her husband alone), and then members of the administration throw large parties at the prime minister’s residence.

Sure, it’s not that bad from an absolute perspective, and probably no one was hurt by it, but the public generally expects individual members of the government to abide by the law no matter what.

Yes, breaking the law is considered committing a crime. It might not be a particularly big crime and likely wouldn't normally warrant more than a warning. But when the people who just passed the law immediately go and break it, the crime itself isn't the issue. The problem is the attitude that the law doesn't apply to those in charge. It is literally the sort of thing that has caused revolutions. People want a just society.

Under convention, a British MP that is convicted of a crime is expected to resign. No Prime Minister has ever been issued a fine or committed a crime before.

Johnson (and the UK treasurer) were both issued a fine for disobeying the COVID restrictions, while in Number 10 (and 11) the official residences.

They offended numerous times, including immediately before a press conference to deliver more onerous restrictions, and before the funeral of Prince Phillip, where the Queen (like many others) was mourning alone.

The Queen wasn't required to keep the COVID restrictions (she is literally "above the law"), but she dutifully obeyed them.

It's not the nature of the crime, it's the complete lack of remorse or even the perception that there was any harm.

Ok. (Police charging someone with something doesn't mean guilty, but fine.) I haven't followed it, I think it's unintersting, I was just explaining what other commenter was referring to.