Why are the Main 7 still in high school?

[Octavia Scratch 153]

Why is everybody still in high school? In the first movie, we see three pictures of Sunset Shimmer winning the fall formal crown. (Freshman, Sophomore, Junior) So that fall formal would of been for senior year and then Legend of Everfree came out, showing that they were on SUMMER VACATION!! Then we see them back in school for the series and fall happens again with human Twilight showing that it is a different year so how come they haven't graduated yet?

[Rafa Stary 2,990]

The Human world is full of all crazy conviences to make the plots of Equestria Girls work, lots of things are just not explained, but I haven't seen all of Equestria Girls yet, when I do I'll see if there's anything in it that makes sense or any fan theories, but for now, I bet they had to keep them in high school to make the audience identify themselves with the characters (as I think EQG was modtly made with teenagers in mind), so they forgot or just didn't care about the passage of time, I don't know, I personally wouldn't puch much thought on Equestria Girls of all things 

[KPackratt 275]

I have a theory that the born human Sunset was a student at CHS prior to pony Sunset arriving at that school and at least one of those school dance photos was of human Sunset. Also, considering the fact that our Sunset Shimmer is born an Equestrian being and given how rough the transition from pony to human was for both her and Twilight, it's possible that pony Sunset got held back for failing at History class for not knowing anything about human history when she set foot in the Human World (and given her arrogant personality during the first Equestria Girls film, she likely failed Social Studies too). As a result, she got pushed back to the same grade as the Mane 5 to the point where she was still in school for as long as they were.

My headcanon is that born human Sunset moved to a different city and transferred schools before pony Sunset arrived to the Human World.

As we saw in "Monday Blues" and "Most Likely to Be Forgotten / Forgotten Friendship", Sunset lives on her own in an apartment, so it's possible that she's older than her friends based on that implication, then again, the Pony Mane 6 live on their own and most viewers assumed they were teenagers during the early seasons of FIM, so that might not be a reliable sign of Sunset being older than the rest of the Mane 7. (Also, it's a cartoon and we've seen cartoon characters live on their own at any age.)