Apple didn't go their own way one this - they teamed up with the people who know this better than anyone, from Pixar to Epic.
Apple stands out from the rest of those industry players by historically having much longer range architectural vision. They have also been investing heavily in their devices for many years to support that vision. The processing power of the typical iPhone outruns average competitor by multiples.
Which makes sense, because this is what glTF was designed for.
https://forums.unrealengine.com/development-discussion/conte...
Thankfully, some quotes from Epic Directors can prove me right....
https://uploadvr.com/epic-games-unreal-engine-april/
To quotes the Technical Director from Epic:
“We will increasingly use USD here. Hopefully, we will keep working with Pixar to make it awesome for every use case we can imagine. ”
And,
“The cool thing here is that we don’t need any other separate tools to go from USD to what you’d see on screen with this demo”