Look, it's probably nothing you're doing wrong. Honestly.
I was on dating sites for YEARS, on and off (I have posted about this many times as have been on MN for about as long as I was single!) and although I got lots of interest, never got past first date, or two, and certainly never to a relationship. Lots of people told me what I was doing wrong, but despite trying all their suggestions, in the end what worked was just being myself. And meeting someone who was right for me.
The only thing I did slightly differently was message him first. I had done that before a number of times with others but never got a reply, so it wasn't something I always did. And I'd done it before and it hadn't worked. Just this time it did.
My bf, fwiw, barely got any replies, and no dates. He is bloody gorgeous (not just me, all my friends think so too!) but also lovely, funny, kind, intelligent...he didn't have the best photo on his profile (it made him look nice rather than hot, iyswim) but still loads better than other guys I'd dated...and who I know had been on dates with lots of other women. My bfs profile was one of the best I'd read too...so sometimes it really makes no sense!
If you don't yet have children, I'd say ditch dating sites. If you have a couple of free evenings a week, join a sports club. Or if you're not sporty try MeetUp if they have events in your area. Or a local community group...or church group if you're in any way religious.