Probably because nobody gives a damn about visibility minima, in most realistic scenarios.
When flying, one isn't trailed by another plane containing CAA employees, filming whether you enter the occassional (or the not so occassional) cloud, and measuring the in-flight visibility as they fly behind you. And checking you don't exceed 140kt below 3000ft or whatever it is. And checking you are 1000ft vert and 1 mile horizontally spaced from the nearest cloud, etc etc.