Because I do.
Not fair to my members who support the site, or the bandwidth, and we have enough problems with people trying to sell our content to unsuspecting people, and add to that people who just have to have EVERYTHING even if they never use it. I'm a resource site, and used by my community to serve very badly needed resources to game table authors, and the more people leeching of my site, the less I have for those authors. Don't care about numbers or revenue or anything, just a smallish site that's important to the development of pinball tables.