It’s better to have a diversified customer-base rather than being completely beholden to a small number of big customers that might decide they don’t need you down the line.
Indeed, Google and Amazon have already shown an interest in designing their own silicon (TPU and Graviton). Probably Microsoft too, but I'm not aware of an example off the top of my head.
Upstarts are not easily going to be able to pursue that, so NVidia has a strong interest in supporting them.
