Because it's got nothing to do with his behaviour and everything to do with his politics.
Starmer is conducting a purge of those with actual left wing, traditional labour principles before the election.
The timing is deliberate. It's last minute so they don't have time to appeal and not much time to stand as an independent.
The complaint they dug up on him (no idea of the content) is 8 years old.
While I can't stand LRM given his stance on women's rights, this is fuckery, and it's not OK to run a party like this. It's not democracy.
I must admit I did laugh a little, given KJK's intentions. What will she do now, I wonder?
But, anyway, what a disappointment Starmer is.
Still a zillion times better than the Tories though (who, may I remind you, started the whole GRA reform nonsense in the first place).