Big chunk of mining is in the hands of a few US public companies with access to the fiat spigot
Discussion
I would argue that it’s in the hands more of Bitmain and it’s many white labels.
Hardware naturally centralizes due to benefits of specialization, and economies of scale. You are correct there are even fewer commodity sha hash machine manufacturers.
However it is the mining cos which decide to which pool to point, which arbitrary rules to enforce.