Compare this to something like the playstation 4, which used freeBSD as the base of their OS, and contributed nothing back to the project at all.
The only big UNIX vendor left was Sun Microsystems, and Solaris indeed dominated the 90s dotcom era. Everybody was running SPARC and SunOS servers.
It wouldn't be until the mid 2000s when Linux started picking up the pieces left behind after Red Hat started their server product and certification program.
For a long time, Linux was strictly a hobbyist OS. It later dominated by simply being the last one standing after everyone else fell.
And "for a long time" was actually a fairly short time. Linux began to approach feature-comparability fast, and ran on PCs, not $10,000 workstations (that were getting beat power-wise by PCs).
I think there were likely other factors that made it win out.
But I think that's the main one that allowed Linux to snowball ahead of the other Unix(-likes).