It can come from a claim on future profits which aren't realized, which is the case here.
When does profits don't materialize, the company goes bankrupt, the government rescues it (can't just cutoff power and water!) and everyone is happy! Well everyone but the majority of taxpayers who aren't also shareholders of the utilities...
Because revenue is pure income without taking costs into account.
So you could still be giving away money to cash out that is owed to someone else? If your revenue is based upon fictional income then these privatised public services will become tax payer problems because they can't be shut down.
- buybacks are taxed when a person gets money for their shares, as capital gains tax
- lots of corporate tax is about exactly the opposite of what you say; i.e. reaching inside a company's bank account and taxing its profits directly, rather than waiting for the money to flow out and taxing it as VAT/income tax/cap gains. A huge amount of money and effort is spent on balancing this correctly, with R&D credits, structuring profits to appear in the correct year, etc etc.