But presumably you don’t just stare at the wall. “Humans need something to do” is mainly bound to not just sitting around twiddling your thumbs. It’s the reason we get bored, the brain is annoyed at not having anything to focus on.
It doesn’t have to be literal work, just something you find engaging, be it going for a run, tending to houseplants, or completing your entire video game backlog.
And of course there is variation between humans. Some people cope well with having little to do, others always need to do something they find productive.
Where I live marriage is pretty close to being entirely symbolic. Not entirely, of course. It gives some legal rights concerning inheritance and rights if one partner becomes sick and you need power of attorney, but for a couple of 20-somethings nothing that registered cohabitation wouldn’t also provide.
People still get married. It’s a symbolic gesture, it means something to the couple and to society as a symbol of love and mutual commitment. It is just an expected step somewhere along the line.
The point, as you mention, is whatever you want the point of marriage to be.