They get billions from TV and broadcasting deals. Its not even an issue for me. I get Comcast Sportsnet and Versus and Fios1 so I dont even worry about using those illegal streams. I only use it once in a while if I don't feel like going downstairs (cable box isnt working in my room). But its not the end of the world like some of the people on here are making it out to be. Also its not theft to watch, its theft for the person streaming it.
Versus deal is less than $90 million per season, so about $3 million per team. This is not the NFL. Billions is way overstating it.
Do you think your "its not theft to watch, its theft for the person streaming it" would work if you were caught receiving stolen goods from a store? "Oh, I didn't steal them, I only took them off the guy who did, I knew it was stolen, but that's not illegal right"
Leagues build in fixes to theft into their ticket sales, merchandising etc. It may not seem like theft to you because I'll just assume you don't know better, but it's theft, and it's costing everyone else more, even if they don't notice it