Inheritance and health decision issues do not require marriage....because you still need powers of attorneys and executors and so on, and these are often NOT a spouse or even a relative in the first place.
Thus, that argument really doesn’t hold water. All these things have been handled for millions of couples who are not “married” just fine. So has division of property for unmarried people splitting up.
They don’t. But it’s a lot less paperwork. One little marriage license handles all the powers of attorney and wills. You don’t need executors if your brand of reality is simple. Everything I own goes to the wife if I die, because we live in a community property state and technically I don’t own anything, WE own it all, and if I die it’s hers and all done. Now if I wanted stuff to be more widely distributed, like if we had kids, or I had an ex, or a favorite charity, then yeah I need a will and an executor and that junk. But I don’t, so I don’t. And most people actually live in a fairly simple version of reality.
Yes it can be “handled” with extra paperwork. But it’s handled for TENS OF MILLIONS of couples through a marriage license. And was for centuries before anybody invented palimony and started with the trouble of faking legal marriage.