It was not a version upgrade from Perl5, but instead practically a new language with some similar design principles. So the name was both holding Raku back by associating it with the warts of Perl5, and also holding Perl5 back because people assumed "Perl 6 was the upgraded version so why use the old one". People have been talking for a long long time that the language is different enough to deserve a different name, and things finally seem to have come to a head recently. As a Perl 5 fan and an early ~Perl 6~Raku enthusiast, I'm happy about this change, though it's almost certainly coming too late. Better late than never, I guess.