What was the stated reason?
57:50 of the video. In effect, disillusion with Apple's direction.
Raspberry Pi hardware would be the obvious constraint. Though, that only pushes the question one step further: Why a Raspberry Pi hardware? I... don't know. If you went from Apple devices, it seems like a non-sequitur. There are much, much better options, unless on an extremely limited budget.
But, I also don't know his use case. Does he have a gazillion of them for some (I assume interesting) reason?