As Sherlock Holmes said, “when you rule out all other possibilities, what is left must be true” or something like that.
The only thing which fits the facts are that indeed it was an attempt to arm Mexican cartels. The reason for that just about had to be to push for gun control based on so many American guns being linked to Mexican crimes.
The administration and it’s media allies were already pushing that fiction before they got caught and yes it has been proven to be fiction.
Either that, or they WANTED to arm Mexican death squads for reasons of their own.
I believe the above is closer to the actual quote but not exactly correct either.