Why say "NO"?

I have come across a lot of happenings in relationships and some ended well while the others hmm... the other way in disaster. We believe that a good relationship can lead to marriage and a good marriage can lead to a good home. My concern about some ladies out there is the fact that you spent years with a guy and everything looks perfect until he finally decides to ask the question "will you marry me?" I still don't get it, you spent an average of 5 years dating someone you regard to as you one and all but the day he decides to propose marriage to you, you turn down the offer. Can anyone explain the reason behind this aside that she is a gold digger? Image http://www.cmetvng.tv/2020/02/17/valentines-day-goes-wrong-as-lady-rejects-marriage-proposal-from-a-south-african-rapper-in-public/