Though I'm unsure how differing licenses might have affected this - I suspect that really early in it's development the "copyleft" nature of the GPL Linux didn't make as much of a difference, as from what I remember most commercial uses of Linux didn't come until it had already gained significant momentum.
Copyleft encourages a collaborative relationship between entities because it makes trying to play it close to the chest with IP involve more legal effort (if it's possible at all).
Commercial support for Linux was... Sparse... before the early 2000s.
Agreed, funnily enough GNU tools/compilers also ended up getting installed on a lot of proprietary UNIXes because proprietary UNIX was mostly shit (in user space!). At least most of the ones I had the misfortune to have to work on.
If Stallman had started with a kernel, there would be very few people who had the legal right to run any utilities or apps on the new kernel whereas GNU's utilities and apps (e.g., Emacs) were immediately useful (i.e., without breaking any copyright law or violating any software license) to a large population, namely, anyone with an account on a proprietary Unix system, which explains why Stallman chose to start with the userland.
> If Stallman had started with a kernel, there would be very few people who had the legal right to run any utilities or apps on the new kernel