Because of out of market fans, and those sites aren't always reliable, and not everyone has internet fast enough to stream live content. Blackout wise, thats for all sports, nothing you can do about it. NFL, MLB, NHL also do it.
yeah, I was pissed, and NBA TV Fan Night is annoying, they talk while the game is going on, and its like Picture in Picture mode, very annoying hearing the NBA TV guys talk, and none of the feeds were FS Houston. Wasn't able to watch the feed of FS Houston because of its blacked out for me.