Well, if we stopped stepping over all the red flags we don't want to see we might have a better time of it.
I'm convinced the part of the brain which squeeeeees from being "in love" easily drowns out the part of the brain which systematically identifies, categorizes, and processes red flags.
Lord knows I've stepped over a quite a few myself.
Most people seem to be rather idealistic when it comes to concepts about love and marriage, so having a conversation about "what if?" really hurts their head (and/or heart) in significant ways. My ex and I were like that when we got married (me 22, him 29), as we both whole-heartedly believed love conquers all.
Another factor has to do with our life position when we get married. Often, people marry young, long before they have any kind of net worth to worry about.
Today, at my age, I wouldn't consider marriage without a prenup. As unromantic as the idea is, I learned a valuable lesson from the first time - practicality rules!
Each US state has different laws regarding divorce even though they have a lot in common. Where I am, her education costs, if paid for out of marital funds, would for certain be considered an asset during the divorce and financially considered.
That happened to a friend of mine - her nursing degree was paid for out of marital funds and when they split, her education came out of her half of the split - which for her and her ex roughly equaled the equity in the house they bought while married, so he kept the house and she kept the education. Though, neither of them were anything less than practical about their divorce so they didn't have the "I will stab thee through my lawyer" scenario that happens so often. They were both fair and reasonable throughout, with some tears along the way.