Now an OS without application compatibility is kind of DoA unless there is a very compelling reason to switch. Add in hardware compatibility and it gets even worse.

Much bigger hill to climb then incorporating an existing browser engine into a custom spin of a browser. Even a browser engine from scratch would be smaller than a new bare metal OS.

The OS game is over. Desktop computing is becoming a professionals-only thing. We can talk about pros and cons of Windows, MacOS, and Linux, but it's a shrinking market without room for a fourth player.

Now let's make that OS talk to a graphics card--whoops, no Nvidia for you, peon!

An OS isn't a problem. Hardware support on an OS--that's a huge problem.

With how mature the personal computer market is, this is a very big hurdle.

And that’s not even covering the numerous hobby OSs out there like Haiku, SerenityOS, ReactOS, TempleOS, SkyOS.

Then you have experimental OSs like Singularity too. There’s numerous examples of them alone but I think you get my point. :)