Fear of loneliness for most people outweighs what they see as a “small problem” of sexual incompatibility. Of course as years pass, small problems become huge problems. People in their first major relationship don’t know this, and people who’ve been in a series of short-term relationships don’t know this (or maybe don’t think it would apply in the long term because they’re omg so in love). The longer I’ve been with someone (anyone), the more their little flaws become magnified into deal-breakers.
This is why I’m still unmarried in my late 20s and will conceivably stay that way forever. Unless I meet my one-in-a-million soulmate (and I’ll know him when I see him, haven’t seen him yet), I see no reason to settle for less. To some people, settling is better than being alone.