Most companies aren't Google or Tesla though.
And like I said, it's likely that different solutions will appeal to different use cases. I bet that aside from those custom chips, Google and Tesla are also using GPU's for some things.
Yeah, you need to be doing enough of the work to justify your own design team and fabrication costs. Most companies aren't on that level or doing that kind of specialized work.
I'm not surprised to see such companies going their own way though. NVidia has managed to alienate just about every major partner they've ever done business with and some of those people have no doubt gone on to work with other companies and have steered them away.