Permissive licenses come with strings attached (that most companies ignore): attribution.
With copyleft licenses, nothing say that you have to get your changes upstream: you just have to distribute them to the users. It's not a whole lot more complicated than attribution: set up a repo and put your fork there publicly.
Attribution has its own issues too, like when curl developers faced Toyota owners who were grasping at straws because the curl attribution featured prominently in the car's malfunctioning entertainment system.
Permissive licenses come with strings attached (that most companies ignore): attribution.
With copyleft licenses, nothing say that you have to get your changes upstream: you just have to distribute them to the users. It's not a whole lot more complicated than attribution: set up a repo and put your fork there publicly.