As an unmarried Young Adult (in the Netherlands) myself I can give my 2 cents about why I wouldn't get married; I've simply taken to heart the advice nearly every senior developer would give me; Don't EVER get married.
I would like to gingerly suggest that this is a subject for which you might not want to sole-source your advice from software developers. We are an odd lot.
In essence, the average man living with a female partner would get a "nuisance" investigated, diagnosed with cancer, and (sometimes) treated; while the average single man sought treatment only when the condition was truly disturbing, and by that time it's too late to treat the cancer.
Some of that is just timing, like if the average age of death per the actuary tables is like 79, and your spouse dies at 80, you're statistically going fairly soon as well.
(old joke)