There’s no real need / use case for a new OS. Existing ones cover about everything;
Operating systems nowadays are way more complex than they were, you can’t just pick and write a successful one in a few months, you’ve to support very complex protocols, hardware and lots of different architectures - even for Linux it’s hard to keep up with all the ARM CPUs;
Contrary to popular belief (what the Linux people on Lemmy think) the success of an OS nowadays is tied to ecosystems and applications. Building the OS doesn’t lead to anything if you can’t get companies like Adobe, Microsoft, Autodesk, Google etc. to write the software that people use for it.