Young people get pretty bombarded by divorce horror stories - especially from pop culture. Most divorces don't go to a court and a large number are resolved entirely internally and only seek professional help for the finalization of the agreement... but there are the attention grabbing headlines of someone being left with only the shirt on his back (and like 20 mil in options) on the far side of a really bad divorce.

I also think that culture does play a fair role. I was initially hesitant to marry (as a millennial) because a lot of my friends were being denied the ability to marry who they chose, so I wanted to stand with them and reject the institution. That, thankfully, has been resolved - but I can totally understand people who have mixed feelings on marriage.