Rim brakes work well owing to the high relative velocity of the rim/braking material -- three or four times higher than for a disc brake. It is pretty straightforward to make a rigid system of lever, cabling and callipers. In theory a disc system will be better at all but very low bicycle speeds but it is much harder to design a rigid mount for the callipers.
A rim brake is a disc brake, usually about 27" in diameter. But friction material made from rubber and a ineffective cable pull caliper and effectively no pad area is what the problem will always be. I am sure a decent calliper could be designed and use hydraulics' but oh, it will be too heavy!! The poor dears are frightened of weight.
And then the tyres have no grip anyway, and that on dry smooth bitumen so wet bumpy and dirt strewn roads you do not stop. Or in my case moss!