I think it's because the driver is forced to keep their pedal foot elevated long term.
The passenger can do whatever they want with their legs...
The luxury leg support I would love would be a split thigh support like the one I recently saw at a car show. It let you control left and right side of the driver though extension independently for both height and forward extension. Would be awesome on those all-day, all-night drives.
This one below isn't as nice as the one I saw, but it's similar. It could raise, but also sort of "unroll" to extend forward:
View attachment 1625754