Why would anyone make a lifetime commitment?

The high cost of divorce can make a lifetime commitment more robust.

Committing a crime together and vowing to remain silent produces high costs. Exchanging embarrassing pictures or other blackmailing material can also produce high costs. I don't know this seems like a fake reason, I mean if you wanted to optimize for robustness of long range commitment and set out to optimize for it would you really end up with anything like marriage? Especially since more than 50% of all marriages end in divorce it dosen't seem to be, as it is practised currently, very good at its supposed function.

In addition unlike other imaginable mechanism, this one isn't symmetric unless it is a same sex marriage. The penalties are on average significantly higher for the male participant. This just seems plain unfair and bad signalling though I admit asymmetric arrangements can be a feature not a bug.

Also I seem to be able to maintain long term relationships with friends and family members without state enforced contracts. Why should a particular kind of relationship between two people require it? And even further why a contract that can't be much customized, that (irrational) voters feel strongly about and the rules of which the government via law or legal practice changes in unpredictable ways every few years?

It also helps with taxes, visas and health care.

This is very Amerocentric. When it comes to income and taxes in Slovenia it is much better not to be married than married, because the welfare state (which is used by almost everyone - lower, middle and even middle upper class to some extent) generally calculates most benefits according to income per family member and many benefits are tied to children and teens. It is nearly always better for the couple not to marry. I have friends from several other countries in Europe who have stated it is much like this in their countries as well.

Visas and generally facilitating immigration sound like good reasons to get married. Edit: This last line wasn't sarcasm, as hard as it may seem to believe. I was still thinking of marriage as a legal category not a traditional ritual.