They had a month to level to 60 and gear up, most normal people aren’t into wasting a month to enter a tournament with practically no odds of getting anything. If you die in the tournament your character is done, so naturally the contestants are largely going to be people with some confidence and time to spare.
This is of course a non-US view, I’m not sure how different the laws are there. But marriage is a great one-stop shop that lets you get a lot of legal kerfuffles sorted in 20-30 minutes with nothing but a couple signatures. I don’t think it is a stupid reason, the stupidity comes from all the other bullshit people want to dump onto marriage.