Linux required scale. It being free doesn't negate the requirement for a large group of contributors and corporate donors.
Haiku OS doesn't have many serious users or use cases even after 18 years of development. I really appreciate the work they do but it shows how incredibly tough it is to make an operating system for the masses.
TempleOS is definitely not something anyone uses except to try out the weird OS they heard about. It won't even run on my hardware without virtualization.
QNX made by blackberry, IOS as you stated Cisco for its own hardware, VxWorks by TPG Capital and also an RTOS so not consumer hardware.
SkyOS not in development for more than 10 years and never popular and ReactOS is intended to be binary compatible with an existing popular OS so even though it won't be popular it would be leveraging existing ecosystem of apps and resources.
I don't know what point you are trying to raise with playstation OS.
MacOS is developed by a 2 trillion dollar enterprise.
The point is not that OS can't be built without scale but rather that for a consumer OS ecosystem of applications and other resources and hardware choices are concerns that are really tough to solve without scale and thus the market consolidated to only a few popular players.
I don't know what point you are trying to raise with playstation OS.
MacOS is developed by a 2 trillion dollar enterprise.
The point is not that OS can't be built without scale but rather that for a consumer OS ecosystem of applications and other resources and hardware choices are concerns that are really tough to solve without scale and thus the market consolidated to only a few popular players.