Cyclists don't sit on the "sit bones" (ischial tuberosities), but on the much narrower ischial ramus.

The outer width of a saddle has no real connection to how wide the flat portion you sit on is.


Imagine measuring your ankles, then using that measurement to buy shoes that are sized by the width of the outer sole rather than the last. That's how little sense sense picking saddles by sit bone and outer saddle width makes.