IMHO we can't just say that. Because nothing is stopping us users from paying for email, online document storage, blogs, etc. It would appear to me that greed is one cause, and an unrealistic expectation that infrastructure should be free, or at least an all-you-can-eat buffet, is another cause.

Although if I still stubbornly try to view this through the prism of greed, I note that it doesn't necessarily fall apart. Like maybe a user's wanting something for free is a form of greed, and the company that bases its business model around that, is really just turning that greed to its own advantage kind of like an aikido master throwing you ass over tit using mostly your own energy!

Mind you I don't want to imply or pretend I considered any of this ahead of time or intended it as part of my GP comment.