I think they cut it because they felt that it was a plotline that deserved to be fleshed out far more than what they had. Assuming that the deleted scenes were all the lines Sunset had about being homesick, it would have felt kinda…anticlimactic as she just mentions it twice and then decides to stay. I love Sunset’s character as much as the next guy, so I am actually glad that her biggest question, ‘should I stay here or go home?’, isn’t relegated to a sub par subplot, but will hopefully be the main issue she has to deal with in the next movie.
Though, I imagine that while I would prefer she goes home to Equestria, marketing-wise, that would be a bad decision as she is a huge draw now to see the Equestria Girls movies, so removing her would be unwise. Not to mention, she is the reason for magic being in that world in the first place, and though it is established that the Humane six now have magic of their own, her being the tie to MLP would be odd for her to come back.

HOWEVER. It’s also possible that the subplot was cut because they decided to change the resolution, and the movie was too far gone to change enough for Sunset to want to come home. Why? Well, there is the question of, ’ Where is Human Sunset?’. Perhaps the writers found a way to have their cake, (Sunset staying in human world), and eating it too, (Sunset coming home to Equestria).

As for the deleted scene. It was great, don’t get me wrong, and am hoping to see it fully animated a la My Past is not Today; but I can understand why they cut it. So far in the movies, they haven’t really gone into Sunset’s feeling for Equestria to any great detail apart from “she’s from there, and she regrets leaving her studies under Celestia.” Sunset being homesick would be a great subplot, but personally I don’t think it would’ve added much to FG beyond more characterisation for Sunset _{(feel free to point out how it could, I geniunely what to know how you’d integrate that subplot into the plot of FG)}, thus is kind of a moot point whether or not it should’ve been included in FG.

Sunset being homesick is something I want to see examined in a future installment, if not a director’s cut of FG, because like with magic in the EQG universe, it’s kind of important, even if Sunset being homesick is only of character importance.

what!!! how dare you delete the sunset part! is much much much better