They may be free for subscribers.
But not necessarily free for cable providers.
They have to provide connectivity to the content.
Plus it also takes up a slot that can be used for another channel.
So it also comes down to popularity.
I Want My MTV.... oh wait. That's 35 years old.
I Want My NASA TV.
Seriously Verizon: In an age where we are reaching for the Moon AND Mars, launches occur on a weekly (or monthly, at worst) basis, it is inexcuseable to keep America in the dark.
Free via streaming and on the internet may be good and all, but I'm not just thinking of myself. For some, the convenience of things on the television is all they will do, specially when it comes to entertaining young children. Having more quality programming available is paramount. I'm thinking of the kids who may spend too much time watching TV, and that not being their own fault.