Well, we have plenty of series where the protagonist has an harem of demihumans or monster girls, so I don't really have a problem with the fact that human girls might be OK sleeping with an ogre that looks very similar to an handsome, muscular man.
Is it realistic? I'm not going to deny there is a fair amount of wish fulfillment here, but again I'm so used to the typical "you were kind to me so I'll love you forever" we often see in harems to really be surprised.
Actually, I checked this part in the manga, and