Most marriages that are first marriages for both partners end in death. Doesn't sound like there's a lot of regret there. People want to stay married. Otherwise they wouldn't.
[1] https://www.wf-lawyers.com/divorce-statistics-and-facts/
- Lack of commitment 73%
- Argue too much 56%
- Infidelity 55%
- Married too young 46%
- Unrealistic expectations 45%
- Lack of equality in the relationship 44%
- Lack of preparation for marriage 41%
- Domestic Violence or Abuse 25%
(Respondents often cited more that one reason, therefore the percentages add up to much more than 100 percent)
All of those seem like regretful reasons to me. There's no evidence that unregretful reasons are a significant factor in divorces (even anecdotally I've never heard of this, but if you know one then I'd find that pretty interesting). Still sounds like there's a lot of regret out there.
My point is, there is an expectation that a happy marriage lasts your whole life, and while there is nothing wrong with a marriage like that, it is not the only happy solution. You can have a relationship end without regretting ever going into it.
Every aspect of marriage hinges on it not ending before death. All religions explicitly spell that out one way or another. Religion aside, legally every government imposes life-changing financial penalties for ending it that way. The main reason governments do this is because culturally it was very common for the wife to stop working or stop pursuing a career in a marriage due to the implied commitment the husband has to the wife, but if the wife knows that the relationship has a 5 year clock then she would behave differently. Married couples have children due to the implied permanence of their relationship, if a 5 year expiration date was known upfront it would change behavior because it's well known that divorce is damaging to children.
If I buy something called the Forever Car that's very expensive but promises in return to never break down, and then it breaks down in the middle of an interstate trip...I guess that doesn't invalidate all the miles the Forever Car got me through, but it certainly calls into question the value proposition of the Forever Car. I may not regret that I bought a car but I certainly wouldn't have gotten a Forever Car. I would definitely say that a Forever Car that doesn't go the distance has something very wrong with it because it doesn't deliver what it promises.