It's the only general purpose OS that's both on several planets and usable on commodity computing hardware, as opposed to a real time OS or the custom operating systems that predated them. They have a much longer history in space: VxWorks has been on every Mars surface mission since the Pathfinder Lander in 1997 including Perseverance, New Horizons flew by Pluto in 2015 running Nucleus OS and RTEMS is on the Mars Reconnaissance Orbiter.
Sounds right; you can’t open Windows in space.
In space, no one can hear you phone home.
vxworks claimed that title. Unfortunately, Linux never was the "only OS with an installed base covering several planets".
And if you never heard of vxworks or QNX, that's the point. They just work and that's the point.