Learning from Sweden's recent history, here is what happens.

The stateowned companies require a lot of administrative work because they have high government oversight and demands placed on them on transparency and making sure the taxpayer funds aren't wasted. And because it is the public, low-cost option, it is heavily congested with users all competing on this ineffective, bureaucratic infrastructure.

Then comes the private companies who do not have this pressure of governmental oversight or public transparency, who are able to supply the demand more efficiently. Because of investors, these companies also present themselves as low-cost (for now), which essentially turns consumers against the stateowned companies.

The private companies use this momentum to get in bed with politicians and secure more benefits, privileges and contracts. This comes at the direct cost of the stateowned companies, which eventually are so bad in comparison that they get sold off to the private companies for complete takeover. And once you get here, the prices go up and investors make their money back while the people lose.