Why the nuns in the hentai games are always thus pretty ?

Because you wouldn't make any money off a hentai game where the nuns were ugly.

this is one of the reason, but I meant to say that they do not exist in reality unfortunately...

Spoiler: most things depicted in H games don't exist in reality.

葉月 said: Spoiler: most things depicted in H games don't exist in reality.

And that's one of the main reasons we play them.^^;