Because paying for cable means people get jobs, and it means broadcasters get revenue from advertising that the viewers see. If everyone went to downloading stuff from BitTorrent. how long do you think it would be before there was nothing to download because there was no money for new shows? What you get for free costs somebody else something.
I download shows from BT as well. Not because I refuse to pay for cable. I'd rather sit on my couch and watch TV than sit at my computer. But because I don't have cable. Ad I don't have cable because I did not like how the one cable company serving my city was doing business, so I canceled it, along with their internet service. Since I live in a townhouse, I am not allowed to put a dish up, and Bell Canada doesn't offer their TV service through the phone line in my area. If they did, I would have that. So I am stuck with nothing. so far it's been easy, but hockey season starts in a few months, and not watching the games will be lame. But in this case it is a matter of principle rather than just wanting something for nothing.
Even when I move where I can have a dish, I will have a paid service, along with grey market dishes swiping signals from US providers. And "free-to-air" signals as well