It already is a monopolistic entity
How is it?
Only Steam forces you to install their full software package and takes over your game installs in order to activate a game that you have already PAID FOR in a high street shop.
Only Steam makes you dependant on having their software installed and continually running to continue playing the games that YOU have already paid for.
Only Steam makes you agree to a EULA that is illegal in most EU countries in order to play the games that you have PAID FOR.
Only Steam States that if they go tits up they can ply a patch that will make all your "Steam powered" games none Steam dependant, a patch that can do that? Really? If that was so, the pirates and hackers would have already sussed it and done it.
So Steam's not a monopoly?
Yeah right.
Stop letting the fact that you like Steam blind you to the facts about it.