Cable TV in the US from day one had ads, as it was literally just the broadcast networks which had ads repeated on a wire. So no, cable had ads from the beginning.

Then, decades later, the first cable only stations started appearing. Some had ads from the start, some didn't. Some charged extra fees (premium channels), some didn't. Many of the early cable-only channels had ads on day one, some added ads later.

In the US at least, there was practically never a time where there were no ad-supported TV channels on cable. There were always at least some channels that were ad-supported.

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.