Is the devs of different projects working towards same or different goals in different projects?

I'm not a dev, but I am trying to understand why there are so many different projects while all of them seems to share same frontends or UIs or DEs. Isn't the biggest work to be made in the firmware and kernel side? Hopefully the unified bootloader sees the finish line to make porting easier for new devices.

Is there a mobile-only flatpak under development?

I know this all is very confusing to answer, but I fear that fragmentation at this points leads to wasted resources because project X dev doesn't know that project Y is working towards the same goal at the same time. Also multiple different projects makes end-users confused. Which distro to choose, is what my friends often asks me for desktop and now for mobile.