"Because as you know it would have to be much more expensive."
Which is what my follow up point was about. They want people who don't watch BBC to pay so that they spend less. Don't we all want other people to pay for our stuff? Most of us don't get to threaten people with jail unless they comply though.
Note: I don't pay the telly tax and we don't miss it in our household one bit. Advert free Netflix and Prime are top notch.