Because electricity is free. And internet is also free. And the rooms to put the servers are also free. A/C is free. And backup generators are free. And diesel is free.
Of course self-hosting on real hardware is not quite as simple or cheap as GP made it out to be. But everything in your post can be solved with simple fixed pricing, which is still the main point: there are no dangers of wildly variable pricing or accidental massive bills as there are with cloud hosting providers.