Definitely read up on the Torvalds/Tanenbaum debate as there are lots of moving pieces and interesting theories. My opinion summed up ridiculously concisely is

Definitely read up on the Torvalds/Tanenbaum debate as there are lots of moving pieces and interesting theories. My opinion summed up ridiculously concisely is that the reasons are largely accidents of timing (i.e. there was room in the market for new entrants), mixed with trivial-at-the-time but high-impact choices. Had Tanenbaum been permitted by his publisher to give away copies of minix freely, Linux may never have been started at all. Had Tanenbaum chose raw performance over teachability (the kernel was a teaching tool after all), it may have made a difference. (warning: this part is controversial) There's also a lot of question about whether the GPL licensing kept Linux relevant, or if it was largely inconsequential. My opinion is that GPL made a big difference. Had the licensing of Minix been GPL flavored, it probably wouldn't have been used by companies like Intel for the Management Engine, but there might have been enough "forced sharing" to keep it relevant. Impossible to say for sure, but that's my two cents.