Lets face it people stay married because (they) want to. You don't have to be "happy" to have a long lasting marriage.
Awhile back I heard a young female radio host ask a woman who had been married for over 50 years; "What's the secret?" The elderly lady responded by saying, "Baby, we just stayed together."
Maybe this couple you're talking about will adjust to one another over the years and come to accept each other's differences. Ideally you want to know if you're compatible with someone BEFORE you marry them.
However if arranged marriages are customary in one's culture and they (agree) to following those dictates then they are living life on (their) terms.
“Love isn't finding a perfect person. It's seeing an imperfect person perfectly.” - Sam Keen