On the countrary, there is a lot of evidence that people who "settle down" have lower levels of stress and overall live a better life.
It might not be causation but correlation, but nonetheless, you are wrong. Marriage is definitely a long-term win. For the short term, there is Tinder.
This might be an issue of idiom - "settle down" and "settle" do not mean the same thing. The latter refers to disregarding reasonable qualms and known issues with a potential life partner and going ahead anyway, more or less on the theory of "oh well, where am I going to do better?"
Doing so can work out in the long run, I suppose. But it very often doesn't.
