It was mandated in response to the Firestone scandal/disaster. Over 200 people died because Ford intentionally under-inflated Firestone tires on the Explorer. Also, the tires weren’t very good in the first place.

I guess it got everyone thinking about how dangerous under-inflated tires are on the highway. My guess (and it is a guess) is that radial-velocity pressure estimation wouldn’t have been precise enough and would have either tolerated dangerous under inflation or annoyed with false-positives.