I don’t disagree with what you say. But why did Linux work on all that hardware? I assert that if you trace that line of thinking to its conclusion, the answer is the GPL.
Many people and organizations adapted BSD to run on their hardware, but they had no obligation to upstream those drivers. Linux mandated upstreaming (if you wanted to distribute drivers to users).
That's actually true, if they wanted to distribute a linux compatible driver they had to make it available for anyone to upstream it in the linux kernel.
Probably GPL was indeed a factor that made device makers and hackers to create open source drivers for linux. I am not convinced that it was a major one.
Many people and organizations adapted BSD to run on their hardware, but they had no obligation to upstream those drivers. Linux mandated upstreaming (if you wanted to distribute drivers to users).