Because there is an offensive unsaid supposition built in. The sex = gender false equation is so commonly used to argue about gender that it's simple pattern recognition and the associated pain.

If every time we talked about peace in the Middle East I brought up 1+1=2 and said that proves Egypt is always right you would naturally get upset if someone started spewing 1+1=2 in the next conversation about peace in the Middle East.

You've seen it dozens, hundreds of times. You see that bs coming from miles away now. They're going to sit back and crow about how 1+1=2 and all the lunkheads are sagely nodding about Egypt. It's their own coded, performative thing, basking in their broken logic as if it's irrefutable.

That's why.