Why can’t people just use they/them instead of trying to guess my gender?

I’m AFAB but I have a fairly male presenting haircut. I dress pretty neutral (not dresses) so people just assume I’m a guy. I hate it when I’m either meeting someone new or a stranger and they assume I’m a guy. Half the time they just stare trying to figure it out. I’ve literally had someone say to me “I’m going to kick you in your balls.” What I don’t understand is why people feel like they have to guess. If you’re not sure why not just use they/them? It avoids having you to assume things based on how they present themselves. I’m not expecting everyone to magically know that I I’m nonbinary. I just don’t get why so many people would rather play the game of guess my gender than use neutral language. It would make so many interactions much less awkward.