Theory Why Scootaloo can't fly... Magical biology.

After many seasons we finally see Scootaloo's parents. An Earth Pony father and a Pegasus Mother. There are a few things I noticed, her mother doesn't really fly. Her father is a large muscular Earth pony.

Let's look at this further. First is Mane Allgood, tall lean body long legs, and rarely if ever flies. It's possible that her lack of flight is genetic. We also rarely see other pegasi with that type of body. We do see one pegasus with that body that flying the other are on the ground, it is possible that pegasi with that build aren't good flyers. case in point Fluttershy when a foal had longer legs and was teased for being a weak flyer. In this case, she grew out of it. We can take that perhaps Mane Allgood's Pegasus magic is weak.

Now let's look at her father, Snap Shutter. A large build Earth Pony, clearly strong given how he tackles a crocodile in the last "The Last Crusade" so we can assume his Earth Pony magic is very powerful.

Now comes Scootaloo, if she has more Earth Pony magic in her and weak Pegasus magic, it could explain why she can't fly. Her magic is mixed and the magical traits for Pegasus flight are being overpowered or missing.

This just a theory.