Reincarnation takes a long time. And if you think about it, there's no guarantee if the reincarnated human will be a human in his new life. In the slim chance that he is a human, what are the chances that he falls for the god again? If he dies again, wouldn't that be just an endless loop of sorrow?
The loser is the God. Always waiting.
I guess it depends on how the writer views reincarnation and fate/destiny. It can seem sorrowful if you look at it as a glass half empty situation. To me, I would take it as a see you later situation so their death wouldnt be as sad and being excited to see them in their new life and fall in love again.
Being excited to fall in love aside, the sadness that will eat me away when my beloved looks at me like I'm a stranger when meeting again in his new life... I don't even want to imagine it.
All I'd want to do is to run into his embrace, hold him close and sob. But, if I do that, forget the chances of him liking me, I'd be put in jail.
I hope this doesn't happen to our guy over here.

It's an honest thought to thing about when marrying a god. Human will die. What will the god do then?