Anecdotally, most people hated the Steam Controller's touchpads, and I'll admit I wasn't a fan at first either. But the ability to remap them to be: sticks, trackballs, d-pads, bring up (multi-level) radial menus, etc. is an absolutely killer feature.
I think one of the reasons they "failed" is because they absolutely were not plug-and-play, because to truly utilize their full capabilities, you had to configure them per game.