Linux succeeded because of these reasons:

1) Over time it changed and morphed to include every feature people wanted. It started as a 386, single core kernel whereas now it supports every processor and 1000s of cores.

2) Linux always had the least amount of friction to get stuff working. Back in the early days, trying to get any rando program to compile and work on SunOS, AIX, HPUX, etc -- it was a touch and go / pain the ass process. IF your system had a compiler, you were probably missing any number of dependancies. Linux, you could always get stuff to compile and work.

3) Desktop - Yes, the "year of the desktop" hasn't happened. However, the 30+ years of trying has yielded the best options for a *NIX based environment.