Getting married and using bank services are not strictly optional. I would rather say they are close to necessity. Live-in relationships are not stable. So if you want stability in your family life, then you have to go for marriage. But the risk will always be there. In case of a divorce, be ready to part with a large portion of your wealth. Regarding taxes, there is no escape unless you can find some loophole which is 100% legal.
You maybe right about that it is close to necessity, but still it is an option. Not all individuals are looking up to be married or to be in a relationship. Some are wanting to be by their own by the rest of their life. Also, not all are trusting banks to put their wealth on it. They just manage to put it on any trading or keeping it in their own place. Think out of the box because not all are having the same principle, goals, ambition or motive.