Probably because a lot of people who are attracted to lemmy might have loved the freedom and anonymity that old reddit offered them back then and this interface reminds them of that. I for one have fond memories of how reddit was a decade ago and it's been a while since I've seen a social network like that. Everything these days are so facebook like.
Hey, it's not your fault.
If you are a guy, and you don't look like Brad Pitt, online dating is depressing. If you happen to look like Brad Pitt, it can still be pretty hard.
That's just how it is structured. People approach online dating looking for short term distractions. Try setting up a profile saying something like 'I am looking for someone who is willing to put in the hardwork through all the arguments and the compromises and adjustments we will need to make a marriage work' and see how much success you have.
You could be doing everything right and you still will end up getting matched with a lot of people who might not be as serious as you might be about it. That's just how online dating works.
I have only seen the instance on mlmym.org, not a lemmy instance, maybe an instance of the UI. Never seen this mentioned anywhere else.