Why is it called Perl 7?

Short version is "so that we can change the defaults". Turn on strict and warnings and enable say and so on without requiring a bunch of boilerplate use statements to enable everything that's been developed in the last decade.

I think a lot of it is also marketing-driven, to indicate that "this is the latest Perl" and avoid managers saying "Why are you using Perl 5, when there's a Perl 6 out there?", but changing the defaults is the stated official purpose of Perl 7.

Doesn't that seem outright ridiculous considering the fiasco of Perl 6?

Contrary to the suggestions in the root node of this discussion, Perl 7 is supposed to only be "the latest Perl 5 with different defaults" and not a Perl 6-style complete overhaul of the language.