I think a big part of it was the community that formed around the Linux brand. I have a feeling that it could have been Minix, if it was properly open source at the time. But a lot of people in the community were promoting Linux as an alternative to Dos/Windows (based on my recollection of Usenet and BBS postings at the time), whereas GNU, BSD were pushed as an alternative to Unix. And Minix's aim was educational, although Minix 386 (a set of community patches to the system) was more aimed to make Minix production capable.