Making the removal of ads a feature of a paid product is (or was) a common pattern but it's not any sort of law.

You can still get cable channels with no commercials, I have a handful of them despite not paying for the HBO tier. And DVRs make commercials on other channels skippable. Streaming tech was always destined to take away control of the video stream so that commercials would become unskippable. That's what's at the root of it. Predictable, but not illegal.