And most importantly for a runtime format, glTF is fast and easy to load. It's specifically designed to mirror the capabilities of real-time 3D APIs and allow mesh data to be memcpy'd directly onto the GPU with zero processing at load-time. On the other hand USD/USDZ doesn't even attempt to be GPU-friendly, given it was designed as an exchange format for production.

Also supported in products already by Facebook, Google, and even Microsoft. Really disappointed that Apple went their own way on this.