You could ask Norway what's the point of their sovereign wealth fund, I guess.What would be the point of having a state owned company making a profit to return to the state? May as well have it charge less, make no profit (but cover it's running costs) and we all pay less in the first place.
Seriously, the point is that companies that people argue should be state owned are ones that also end up taking massive amounts of public funds anyway, water power, health, telecoms etc, etc.
If the Public are paying when infrastructure is needed but not profitable, then it should also benefit when the companies are profitable.