I heard an interesting theory that you're more likely to go on dates with avoidant personality types. The secure ones are not bouncing in and out of relationships.

Dating is a "market for lemons".

https://en.wikipedia.org/wiki/The_Market_for_Lemons

That's pretty rude. People are single for all sorts of reasons that don't make them "defective".

Read the article. "Markets for lemons" contain both "peaches" and "lemons". There are just forces acting on the market to keep the "lemons" there.

Probably sort of like hiring - everyone always complains most candidates are bad can't even do fizzbuzz, etc- presumably because the good candidates are happily employed.

Yep, and when they're not - they never hit the public markets. They get snapped up on a referral instantly.