Are they so different that it’s justified to have so many different distributions? So far I guess that different package manager are the reason that divides the linux community. One may be on KDE and one on GNOME but they can use each other’s packages but usually you are bound to one manager
People have different opinions on how packages should be managed. Of course, there are some package managers which are very similar to each other (DNF and zypper have the same backend), but they can also get really different (Nix/Guix and pacman are basically completely opposite in philosophy). It comes down to preference, and you can’t force anything.