1. Users post things pirated (live sports streams) because they cant get it from the producers. 2. Producers sue the service that enables this. 3. Producers realize that they should actually help enable this in a legal manner instead of preventing it. 4. Producers partner with the services and offer the content for a price or ad supported. Piracy still continues, but at a slower pace and the content producers are getting paid in some form at least.
Most sports have internet streaming tied to their broadcast deals which prevents them from being fully streamed.
Slight edit for those who don't know. There are Over The Air HD antennas. If most of your sports content is on one of the big networks (football, some basketball and football) or on a local over the air channel these work pretty well. I have one plugged into my HDTV/Monitor at work and was able to get HD football on it pretty damn well.
Check out http://atdhe.net/