FAT has serious limitations wrt filesizes, it is not good enough for interop use. Even Microsoft's own Windows install media has a problem with it.
exFAT is better, but it is also quite recent development on Linux, since it was licensed and only in 2019 that Microsoft publicly said, they would not ask for any licensing and the specification became publicly available.
Both of them are quite unfriendly to flash memory, but exFAT is good enough.
File permissions usually don't make sense on an external drive that's moving between computers, much less computers running a different OS.
I just don't see why it's surprising that Microsoft and Apple don't have built-in support for ext when FAT/exFAT support is good enough for 99% of interop use cases.