To use an analogy, imagine you’re fat and trying to lose weight. Someone admits they are attracted to you, “sure, as long as you’re still fat”. Can you see how this would not be a good basis for a healthy relationship? You could even say it is a sign of a “chubby chaser”. Likewise for transness.
Also, people are overly sensitive because being denied full/legitimate relationships is a frequent pain point for trans people (esp trans women). The classic trope is the boyfriend who will take you on dates but refuse to introduce you to his friends/relatives.
So yeah, I can see why a queer friendly instance would defederate an instance whose admins promote/defend that sort of rhetoric. Hexbear might have jumped the gun (as I told them at the time) but the blahaj admins weren’t great either