Or opponent is feeling mercy for myself and thinking... This guy won, let him go away happy... or he may think "He lost, but I don't want to beat him again...
Why does no one accept my rematch?

I never said they were under obligation.
You just called them "cowards" for doing the most natural thing in the world (playing another chess game against another player).
Yes I did. And thats what they are. The most natural thing for a warrior to do is go head to head with his opponent to see who is stronger. The natural thing for a coward to do is run. But again I never said anyone is obligated to rematch.

To go head to head and see who is stronger? Funnily enough when these people lose they are keen to play the same person again lol.

Lol.Perhaps feel as Challenge.Insistence.But that's can work emotionally not so Good I opine.Perhaps is best idea to add to friend and wait other moment and prep again.In other way, emotion of moment can be used as energy to try the victory.Not my case.So far of feel bad or frustration,if rival deserve victory is good to me.
Agree that we are making imagination exercises.I use the term "perhaps".Also is posible that he won the lottery or something and go to celebrate.Or the tea or cafe falls,or the rival remember that is on tv their fav serie or music show.Can be a clasical.Oscar winner or comedy.Thats happens just on the moment when you send remacth petition...