From my experience people tend to date within the fandom because it's a place where you'll meet someone likeminded. People who are nerdy, creative and tolerant. It's definitely a spectrum - one one side you get those who are furry-adjacent, and then there are those for whom furry forms a big part of their life and they'll go to lots of cons etc. For the former, I'm sure they come into contact with plenty of potential partners in similar nerdy groups (who aren't necessarily furries) but who share enough common interests that dating 'outside the fandom' is quite possible. But for the latter, surely you'd want to date another furry so that you can enjoy furry conventions and events together, seeing as that takes up a lot of their spare time.
I don't think furries set out with the plan to specifically date someone within the fandom, but it just happens naturally when you're in constant contact with the fandom.
You seem to be saying that people should lower their expectations and just date someone even if they're not attracted to them. I... don't really agree with that. I think you should date people that you get on well with. There are plenty of people out there - just socialise with others and it'll eventually happen.