- Being the kernel of ChromeOS and Android, not accessible to majority of userspace and easily replaceable by anything else (e.g. Fuchsia).

- Lost to macOS and Windows on the desktop

It only won on the server room, and now it runs under Minix supervision.

If it's so easy, why hasn't it happen yet?

Linux comes mostly for free, Fuchsia is still not mature enough and is 100% on Google's budget.

However and this is what I always raise up to people rejoicing about Linux on Android, using official Android images, there is very little Linux exposed to application writers.

The Java Frameworks are naturally kernel agnostic, and the NDK APIs are quite constrained, with the main goal of being used to implement Java native methods or bring in C or C++ code into Android.

https://developer.android.com/ndk/guides/stable_apis.html

https://developer.android.com/ndk/reference/index.html

Anything else just isn't allowed and might kill the app as of Android 7.

https://android-developers.googleblog.com/2016/06/android-ch...

https://android-developers.googleblog.com/2017/07/seccomp-fi...

Hence why Termux needs to emulate many Linux behaviors.

Said differently: Linux works and is useful for everyone and has wide corporate backing, while Fuchsia is only useful to Google.

I'll put my bets on which one persists in the long run based solely on that premise.