User blog comment:BlackWizardZeref/Fairy Tail Chapter 382: Alegria/@comment-24748439-20140501015948/@comment-7418318-20140501142731

Now that's a reasoning I can understand and can even relate to.

Though I'd like to point out one thing:

We don't know if another mage ever collected all twelve.

Considering that there's this legend that the twelve golden keys united will open the gate to change the world (or whatever it was colled exactly), I'd even go so far to say that we have one hint that someone collected them in the past. Far from proof, but still a tiny hint. Of course it could also be that this information is just wishful thinking, theoretical information from Crux, a baseless fable or somehow related to the Eclipse (though Yukino didn't know about Eclipse at that point, so I find that highly doubtful).

Then there's also the matter of the location of the keys. Fiore is just one comparetivaly small country that's only a tiny part of the continent and even smaller compared to the entire world. So why are all of the golden keys concentrated in this one small country? After all there are "only 12 in the entire world". If it is just chance, then I think this is the point we should call bullshit, rather than Lucy getting them.

Putting pure chance aside, it could also be that they are somehow tied to the country or terretory... or it could be a hint that in the past someone managed to gather them all and brought them to Fiore and after this person's death, they weren't dispersed too far.

As for the other side, we have neither proof nor even a hint. At no point in the story is it ever mentioned that no one collected all the Zodiacs.