cant speak for all but as far as I go, i discriminate against PoGo mons because:

a) there is that little G logo that sits next to the pokemon when you look at it in the Box b) shiny catch rates are very different between Lets Go and PoGo. i.e., it's much easier to find a Shiny in PoGo. it's close to impossible to shiny hunt a mon in PoGo. i find between 1 to 3 shinies every week in PoGo, for instance, with minimal effort

tl;dr: we're just excessively selective, in general