Honesty this just seems that we’ve lost a lot of operating systems except for POSIX and NT. Imagine a libcurl for a SmallTalk machine… or a custom RTOS without any POSIX comapt layer; I’d bet Windows will seem easy compared to one.
In fact, maybe the fact that a Windows port of libcurl can exist at all means that the Windows BSD socket implementation is useful enough to allow these sort of things.
Symbian was the last weird built-from-scratch OS that shipped a massive amount of units (over 100M in 2010).
In its last years it got a POSIX compatibility layer. Before that it was hard to even use C strings — which I presume was considered a feature by the Symbian API designers, but unfortunately they made their design choices in the mid-1990s using a subset of C++ that didn’t age well at all.
FWIW Nintendo's Horizon OS is also built from scratch (and isn't Unix at all), and has also shipped on a massive amount of units (over 110M as of 2022).
But the point is that crazy thing was not what the developer said was the hardest to deal with. Doesn't matter much that it's closed or not many developers see it, he does.
Linux is both older than Symbian and wasn't designed from scratch since it's derived from Unix. So I guess it's a philosophical question whether Android is Linux or something new.
Linux is just a kernel, and only a Unix-like kernel at that. It is not an operating system. You're probably thinking of the GNU/Linux operating system, but then GNU is a recursive acronym for GNU's Not Unix. Android forgoes the GNU part, but maintains the Linux part (albeit with some patches).
While both written from scratch at some point in history, the trouble is that Linux is the newer one. Symbian is rebranded EPOC, which is older than Linux.
In fact, maybe the fact that a Windows port of libcurl can exist at all means that the Windows BSD socket implementation is useful enough to allow these sort of things.