What's the difference between package manager and why are there so many?
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
Because people will never agree on a single one, and it's FOSS so nothing is forced. I for one am glad I don't have to use apt because I prefer pacman, just as I am glad someone who doesn't want to use an Arch-derivative has Debian and apt to fall back on.