Early Linux was a university student having fun in his apartment learning 386 assembly, and everything onward from there was earned by merit (it just was that good). This is boasting to be "modern computing reimagined", "the future of computing", "revolutionary operating system", "designed to power the next generation of modern computing", "redefining what an operating system can achieve". Burden of proof is on a slightly different level.

Being an Open-Source, free OS was the Linux selling point, over commercial Unixes and Windows. That was the open lane with relatively little competition. Now that Linux and BSDs are there, it's no longer an empty lane but a tough one to compete in.

Granted FreeBSD could have picked up more instead, but it was almost as young and not to be due to a series of 90s decisions (BSD court case; Linux name being catchy; Linux running a bit better on 386 PCs?; GNU tools being the default?; IBM deciding to invest in Linux).