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.

I believe the issue was that Perl 6 had too many changes that made it hard to convert apps from earlier version.

That created some kind of limbo where people weren't sure if they should use perl 5 or perl 6 (”why develop in perl 5, when it is probably a dead end and perl 6 is the future” and at the same time "why should I convert to perl 6, what if it will be a failure and I wasted my time?")

By renaming it, it revives Perl 5 so developent can continue, and at the same time Perl 6 is presented as a new language, now whichever wins will be based on its merit.

Also, importantly, reflecting that they are in no more competition than Perl and Ruby are.

The sibling comments aren't wrong. However, Perl 6 was originally intended to be the next version of Perl. For a long time it was vapourware, however, and development restarted on Perl 5.

When Perl 6 finally arrived, it was too much of a step change from Perl 5 to convince many people (myself included). Meanwhile, Perl 5 had continued to develop and was, in no way, in need of a replacement.

Perl 6 sounds like a successor of Perl 5 but in reality it is a totally new language. Many long time Perl 5 users think a new name for a new language would have been better.

The name Perl 6 was damaging to the popularity of Perl because beginners were confused whether they should learn Perl 5 or Perl 6. The same confusion existed in Python: Python 2 vs. Python 3 but the Python Wiki was always very clear. Until a certain point, it recommended Python 2 and after Python 3 became very popular, it recommended Python 3. That sort of clarity was missing in Perl. Due to the number of new programmers learning Perl decreased rapidly and finally Python overtook in popularity.

Thid said, Python 2 vs 3 did not matter for a beginner. Beside print they would not see a difference.

I started to use Python when 3 was taking off. Did some code on 2 for a few months, then just swapped the interpreter without any modification of the code (beside print).

For advanced devs the story may be different.