We can insist everyone self-hosts everything, but is it worth it? Do you have your own email? It's quite normal for a government agency to contract a third party to supply e.g. furniture, instead of chopping its own wood.
I think the comparison is fair enough considering that self-hosted would work sort of similar. In that you'd rent the physical space for your hardware (and possibly the hardware itself) at local suppliers, and not actually have it in your basement.