Given the same rough patch in a relationship,why do ppl ume the demise of a marriage , but not that other?

What I'm saying is ppl in intimate relationships do face the same problems as married ppl , and they even drag on in it , I mean try to stay together even without such marital commitment, but why do they jump at the first opportunity of seeing a marriage in a rough patch and point the finger to say it's not gonna last? Why double standard?