It's telling that you've neglected your own labor in this assessment, and that of the other specialists required to get such ad-hoc compute working at scale (dynamic software networks, on-demand compute, provisioning/billing/monitoring apparatuses, etc...)
What plenty have realized in cloud-native approaches is that the TCO is pretty compelling, sometimes because its easier to distribute procurement/provisioning/billing to teams for their own resource needs, or just in sidestepping the inevitable bureaucracy when you try to centralize that decision-making.
Of course its different if you're talking hobby kit setups in our own homes, but if you're aiming at real scale for absurd parallelisms then that ship has sailed.