OCP hardware is only really accessible to hyperscalers. You can't go out and just buy a rack or two, the Taiwanese OEMs don't do direct deals that small. Even if they did, no integration is done for you. You would have to integrate the compute hardware from one company, the network fabric from another company, and then the OS and everything else from yet another. That's a lot of risk, a lot of engineering resources, a lot of procurement overhead, and a lot of different vendors pointing fingers at each other when something doesn't work.
If you're Amazon or Google, you can do this stuff yourself. If you're a normal company, you probably won't have the inhouse expertise.
On the other hand, Oxide sells a turnkey IaaS platform that you can just roll off the pallet, plug in and start using immediately. You only need to pay one company, and you have one company to yell at if something goes wrong.
You can buy a rack of 1-2U machines from Dell, HPE or Cisco with VMware or some other HCI platform, but you don't get that power efficiency or the really nice control plane Oxide have on their platform.