I see it as evolution, they all explore the feature-scape and find interesting and new ways to interact with your computer. Or they find new development models

I see it as evolution, they all explore the feature-scape and find interesting and new ways to interact with your computer. Or they find new development models or new ways to make money. Some distros are short lived but their ideas may live on as things that stick and increase in frequency in the next generation of distros. I doubt KDE would look as it does without Gnome and vice versa. Ubuntu was also at some point yet-another-distro. Etc.