They can, and some services offer both. Maintaining two systems is resource and support intensive though, especially for payments. It's rarely worth the hassle

They can, and some services offer both. Maintaining two systems is resource and support intensive though, especially for payments. It's rarely worth the hassle if you only get 1 in a million to subscribe directly. The cable-bundle approach to content might get more traction but there are too many competing bundles adding fatigue (just like video streaming), on top of the fact that people don't value general content the same as music or movies so the rates are inconsequential compared to ads.