I don’t think anyone marries someone JUST so the other person can stay in the country. You still look at the personalities, families.. etc. My aunt married my uncle who came to the US as a student, but she didn’t do it as a charity JUST so he can stay here. They’ve been happily married for almost 20 years.
My friend just got married to a guy in a similar situation.. Too early to tell how his behavior will be towards her.. but so far he’s good.