Quite simply, because the guy who first created Perl still wants to call it Perl.

I guess it depends how you define a fork. If you consider a patch set a fork, then most distributions fork a large majority of the software they ship. And for the kernel, there are actually many many forks--it's the development model they actively encourage with git.

Before you paste, turn on paste:

:set paste

Then go to insert mode and paste your little heart out. When you're done, turn paste off:

:set nopaste