I imagine that's largely because PCs aren't really a thing in Japan. They're not a major household appliance like they are here. It probably never even occurred to them to use anything but a controller.
I think the flaw in the touchpad is that Sony never said what it was for. There are no examples of what the designers were thinking of when they made it, they just added it and let the developers do whatever they want with it. Which on the one hand is great, because the devs aren't constrained by only being "allowed" to use it under certain gameplay or control situations. But on the flip side, it seems a lot of devs are just scratching their heads trying to find a use for it. Especially with today's reliance on multiplatform games. Since the other consoles don't have it, you can't build a key gameplay feature around it, and it ends up feeling like something worthless tacked on as a bullet point just for the PS4 version. Assassin's Creed 4, for example. It brings up the map, which is fine (that's just the button press doing that), and you can use it to navigate around the map. But that navigation is clunky, and I've found it easier to just use the regular control buttons to navigate the map rather than the touchpad. So at the end of the day, the only ones using it are the exclusive devs like Guerrilla and Sucker Punch, and even they're using it for more incidental aspects of the gameplay than anything major. Even in Infamous, most of the time you use it to drain power, where it just acts as another button to press. Sucker Punch got far more effective use out of the speaker than they did the touchpad, IMO.
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