Because they can.
And the few fans who'll use this service aren't near TV's anyway.
The NBA knows how to market itself, it's doing the right thing. Just wait streaming to mobile handsets will follow too.
The fact is the NBA has streamed its live games via the internet the past couple of seasons through NBA Broadband.
Its been included at no extra charge with the D* NBA League Pass subscription, but now it sounds like it'll become its own a la carte service.