There’s a huge market for OSes that can consistently run Windows software. There’s no market for a brand new general purpose OS that can’t run anything until software developers port to it. Similarly, nobody is keen to pay anyone for an OS that can run Android or Linux software when they can get that for free.
Is it? There is Wine/Crossover on Linux. Also, users pay for Sailfish OS, which can run Android apps (while providing better privacy).
It's partly that (after all so long as your new OS has a decent browser most people won't care), but also hardware support. Every single driver has some specific hardware's ridiculous and strange quirks and "yeah we comply with that standard except for all the times we don't", and re-writing every Windows, Linux, or *BSD driver for $NEW_OS just doesn't pencil out.