It's probably a little more clear if you realize that in the view of the exchanges, data is what they are selling; or at least it is one of their most valuable products. It is not something like a price tag at WalMart in their view.
When people got together to buy and sell stocks in New York or pork bellies in Chicago, the really great value added to the economy was "price discovery." We all know what a bushel of wheat is worth (for the moment) just because the CBOT has these trades going on. This, for example, would make it hard for the local grain elevator to take advantage of the local farmer. We've got so much price discovery now-a-days that it takes a moment to remember what it's like when you don't know what something is "worth" in the open market. You get a little of the experience when you go to sell your house. Just what is this thing worth? Did I sell for too much or too little? You're never quite sure.
Anyway, the exchanges have prices. That's what they are selling, and they expect to get paid for it. It is exceedingly valuable information to traders. Why should they give it away?
I understand that they are trying to screw everybody for as much as they can. Welcome to capitalism.