Here in the UK, I feel like a similar thing happened with cable/satellite. Originally, Sky TV was completely free. They only had 4 channels (and one of them was only kinda sky) mind you. But they were all free (with adverts). Later they brought in encryption and a subscription for the movie channel.
I am quite sure I recall seeing one of the rationales for when they started the subscription service covering the non movie channel, it was stated that there would be less or no advertising and it would instead be covered by the subscription. Needless to say, that never happened.
But ultimately, this is just normal business practice. If they can get away with charging you AND making money from ad views, they're going to do it. The only way to stop it, is not to subscribe to those that do it.