I don't understand why you think how easy it is to drag and drop files is even relevant to this discussion. It doesn't matter how superior you feel to people who cannot do this. When you run a business, especially in selling games, you cater to stupid people. Steam Workshop will help these stupid people at least realize that modding exists. Once they realize modding exists, they have a greater chance of staying in our in-game community. Then once they start asking where to get things that aren't on the workshop, they get linked here or to Glass. They start to realize that yes, they can just drag and drop files.
If you personally don't like Steam Workshop, don't use it. Simple as that. But you cannot argue that it wouldn't help the game. You can only argue that people are dumb. You're right. People are dumb. But those dumb people have money and time to spend here.