The existence of permissive licenses like BSD or MIT does not show that copyleft was unimportant.Those licenses allowed code to remain open, but they also allowed it to be absorbed into proprietary products.

The GPL’s significance was that it changed the default outcome. At a time when software was overwhelmingly proprietary, it created a mechanism that required improvements to remain available to users and developers downstream.

Gcc was a massive deal for the reasons why compilers are free now today for example