But the large volume of copyleft does make it much easier for all the BSD/MIT/X11/ISC ("permissively licenced") stuff to show up in e.g., enterprise Linux distr

But the large volume of copyleft does make it much easier for all the BSD/MIT/X11/ISC ("permissively licenced") stuff to show up in e.g., enterprise Linux distribution releases, under the "we have to do it anyway for all these other packages, so we may as well do it for all the FOSS code that we use" type of argument. There was a kerfuffle with RHEL a couple of years back, where they tried to provide sources only to paying customers. Not sure where that ends up.