Where have you been, the cave?

Linux community have been solving problems together since the dawn of time, despite the bazillion different standards they endorse on their own, they collaborate with each other.

Take a look at KDE & GNOME. They are opposed to each other on the surface level, but they both share countless amount of work. Also MATE, which is a fork of GNOME that is created basically from disagreement of modern GNOME's direction, still uses a lot of GNOME's library.