The cultural messaging, especially from the left, is less "sex positive" and more "sex-pushy" these days. Hook-ups and first-date sex are presented as the normal, default way to live. (Related is the idea of "vanilla" sex being a boring thing for stodgy religious boomers.) This is regardless of what actual people generally want. People who don't want these things are trying to communicate their style, without being deemed conservative, sex-negative prudes. The tool they reach for is the liberal label machine. It makes sense.

Some of it is for attention, sure. But some is just a way of escaping the pressures of society, and to communicate in an acceptable way what kind of dating partner you want. The fact is "I don't do sex on the first few dates" can sound like a preference that can be overcome by the right challenger. "I'm demisexual" sounds more like a firm warning against disrespecting identity, lest one incur the wrath of wokeism.

It's a label that shouldn't be needed, but to me it's completely understandable why some think they do need it.