Engaged couples have to give in to those emotions though, or the entire fiction of marriage falls apart.
If people seriously thought the risk of a marriage going wrong was significant why would they ever get married? So anyone who actually goes through with the wedding has to be completely emotionally all in already. Arguing against giving into emotions is tantamount to arguing they shouldn't get married in the first place.
The risk of business failure is similar to the risk of divorce yet people don't consider starting a business a "fiction entirely based on irrational emotions." It's not, just like marriage is not.
And since more unmarried couples split up than married couples, you're actually arguing against romantic relationships entirely.
Using this logic, since you usually lose touch with many friends over the years, why have friends at all then? You're probably going to outlive your pet, so why get a pet at all if it's just going to die?
Just because something ends doesn't mean it wasn't worth it for the time it lasted and even if it wasn't, taking some risk isn't entirely irrational.
Do you think it’s at all common that engaged couples would be happy to give up the vow of lifelong commitment (literally until death) or that mainstream culture would agree with you? I highly doubt it. Whatever the pragmatic view you support, neither marriage vows, romantic comedies, disney movies or religion seems to go along with it.
If people seriously thought the risk of a marriage going wrong was significant why would they ever get married? So anyone who actually goes through with the wedding has to be completely emotionally all in already. Arguing against giving into emotions is tantamount to arguing they shouldn't get married in the first place.