But that implies that no one needs a different OS than Windows NT or Unix. People are constantly coming up with reasons to have new programming languages. Are there no reasons to justify a new OS?
Unix, in the sense that we talk about it today, is not an operating system, but a family of operating systems that is based on the original Unix. Linux is Unix in the same way that C is Algol. In the grand scheme of potential languages/operating systems they are very similar, and familiarity with one will transfer well. However, if you consider the ML family of languages (Haskell/Ocaml), or the Prolog family, you will see that Algol/C/Java/Rust are in some sense variations on the same language. In this sense, we have not seen the great variaty of new languages you are referring to.
In the case of OSes, it is beneficial to formalize these similarities into a single API. As long as the operating systems remain conceptually simmilar, there is no point in unnessasarily fragmenting the API. When there is need to deviate from the common Unix system, Unix-like operating systems have no problem doing so. But there is not strong enough reason to through out the massive amount of investment, both in software and human expertise, that has been built up on the common Unix base.
"A consequence of this principle is that every occurrence of every subscript of every subscripted variable was on every occasion checked at run time against both the upper and the lower declared bounds of the array. Many years later we asked our customers whether they wished us to provide an option to switch off these checks in the interests of efficiency on production runs. Unanimously, they urged us not to--they already knew how frequently subscript errors occur on production runs where failure to detect them could be disastrous. I note with fear and horror that even in 1980 language designers and users have not learned this lesson. In any respectable branch of engineering, failure to observe such elementary precautions would have long been against the law."
>Algol/C/Java/Rust are in some sense variations on the same language
Actually, despite its syntax, Rust is more closely related to the ML family than the Algol family. The original Rust compiler was written in OCaml and it definitely shows in the algebraic data types, functional idioms, and immutability by default.
More to the point, maybe a new OS could gain meaningful adoption by seeming superficially like Unix while actually taking significant inspiration elsewhere.
There are plenty of research or toy OSs, but if they try to get really useable, they just implement a Unix compatibility layer and take drivers from BSD.
