I'm really proud of that piece of narrative magic, btw("internet blood"). It came to me in a rare flash of inspiration.
As to the princesses you mentioned, I guess the audience's reception is the key factor here. Perhaps the readers simply require an avatar through whom they can experience that another world. Whatever the case, I wonder what would happen if a portal fantasy story had a relatively memorable main character as opposed to a regular tabula rasa(a self-insert character, basically). How would the genre change? Is the "tabula rasa main character"-trope such an integral part of the form of portal fantasies, that, with a strong lead character, the genre would change entirely? I guess my own story is me exploring this particular issue - among other things.
Back to portal fantasies: I guess we humans have always wanted to experience to unexperienced. To see sights denied to us by reality's cruel bondage. To live and breathe air that is different from ours. Might even be that the said air gives magical powers, who knows...? But like you said, it might be the interaction with wildly different cultures and situations that gives us that interesting experience of travelling to another world. Again, to use my own story as an example - I like to deconstruct things, so Gustav doesn't meet any "new cultures"(in terms of technology or advancement), nor does he travel the seven seas like Sinbad(not sure if the world even HAS seven seas XD). But it's still our main character in a new situation, and we want to see how he adapts to the new challenges thrown at him.
To conclude, I guess exploration is the biggest thing when it comes to portal fantasy. Whatever it is that the writer wants to explore, portal fantasy - as a genre - gives him the power to do just that.
And this is my long, meandering analysis of things done. I'm not even sure if I answered your original question, or thoughts, but hey - I TRIED! XD