Why?

Why update the old, beloved CS:S, instead of making a new one?
the update have ruined the game for so many, so instead of making a new game (which would be much better) and keep the old one, Valve decided to make a major update, the game was perfect as it was. But that way two parts can be satisfied, the ones who enjoyed the old CS:S and the ones who needs something new.
so I have a question for Valve, are you just too lazy to make a new game and just update an old one?