Number of stable Perl 5 releases since the Perl 6 project began in summer 2000: 13.
Number of stable Rakudo (Perl 6 on Parrot) releases since the Perl 6 project began in summer 2000: 17.
Before you tell me how unfair a comparison that is and how you hate my hair and I'm a horrible person, let me add a disclaimer: Perl 5 has several orders of magnitude more users than Rakudo.
Before you get all smug and tell me that I'm correlating meaningless numbers for no good reason, let me revoke part of that disclaimer: in a healthy project, at least some of the users also contribute something back.
The only interesting question to me now is "Why not?"