Why does the software development community fragment itself, particularly the open-source side of it?

. asked: Why for example does it duplicate (divert, waste) effort on designing parallel separate projects like MySQL and PostgreSQL instead of agreeing to continually refine a single standard application?
Why does it come up with Ruby, Python, PHP (and then, separate “frameworks” for all of these as well), etal, instead of focusing on continually refining [...]