why would they do that? not to mention governments are already doing that indirectly by taking equity stakes in some of the companies.

Same reason they should own access lines: everyone needs rackspace/access, it should be treated like a public service to avoid rent seeing. Having a data center in every city where all of the local lines terminate into could open the doors to a lot of interesting use cases, really help with local resiliency/decentralization efforts, and provide a great alternative to cloud providers that doesn't break the bank.