I'm not sure this is true. See LLVM as an example. GCC existing and being GPL only meant that, e.g., Apple couldn't properly use it. Apple could have bought LLVM and kept it private, or develop their own proprietary solution and not make it open source, or fork the open source project into a private project and never contribute anything back, etc. There were many options.
Open source software has always existed, if anything, the GPL demonstrated that a particular open source model does not work well for a big part of the industry, while it works well for other parts, and non industrial usage.
Linux being successful seems incidental to it being GPL'ed, at least to me. Other open source OSes, like BSD 4.x, have also been quite successfull (powering the whole MacOS and iOS ecosystems, after a significant frankenstransform into Mach). Maybe Linux would have been even more succesfull with a BSD license, or maybe it would be dead.