Economics, pure and simple.

SpaceX was heavily capitalised during an era of easy money, so they have cash to burn advancing this technology. Everyone benefits. But there is no indication they are anywhere near profitability. So why would other space programs do this, when they can reap the benefits (tech and cargo) of a VC and government subsidised company?

Or do you think the SpaceX engineering team is the only one on the planet capable of doing this? I'm sure they're awesome, but that's a stretch.