And memory. In the heyday of ATM (late 90s) a few megabytes was quite expensive for a set-top box, so you couldn't buffer many seconds of compressed video.

Also, the phone companies had a pathological aversion to understanding Moore's law, because it suggested they'd have to charge half as much for bandwidth every 18 months. Long distance rates had gone down more like 50%/decade, and even that was too fast.