I would add the the overall level of quality has dropped so precipitously that what isn't claimed isn't worth claiming.
You see someone in the 30s who has never been married nor in a long-term relationship, and you will think “What’s wrong with them?” It’s human nature to think that way. Maybe they were too “career-driven”, or just a bad partner who was incapable of sustaining long-term relationships.
As a result, I believe that makes it very difficult to develop complete trust in such people, that is necessary for a successful marriage.
I used to believe that it was good to wait and “figure yourself out” before settling down, but now, not so much, and it certainly not what I will advise my kids to do.
My advice now is, find someone good enough as soon as possible and make it work.