You would be surprised how many people I have seen try to do this:

MyMooseModule->has(thing => ( ... ));
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as a way to dynamically extend a class at runtime, instead of just (correctly) using the MOP

MyMooseModule->meta->add_attribute(thing => ( ... ));
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I suspect to some degree it is because people are too used to the older perl OO frameworks like Class::Accessor which forced you to inherit from itself and therefore made things like $some_object->mk_accessor('foo') possible, even though that is evil and wrong ;)