At a glance, I'd say:

Perl's DOES defaults to ISA since Perl can't distinguish between base classes and roles/traits.

Moose can distinguish between base classes and roles/traits, so it doesn't need to fallback to Perl's inaccurate default.

In reply to Re^3: Introspection of Moose/Mouse attributes fails to find native trait with `does` by ikegami
in thread Introspection of Moose/Mouse attributes fails to find native trait with `does` by Your Mother

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