"Not one of the 59 or 500 were armed."

And it wouldn't have mattered if all 22,000 at the concert were armed (with anything less than a decent rifle). They were 400+ yards away from and 100+ yards below the shooter.

"And the shooter was not licensed to own a full automatic weapon."

First, there is not yet any evidence that he owned any full-auto weapons. He had 12 semi-auto rifles with bump fire stocks.

Second, no license is required. Just a $200 tax stamp per firearm. (Unless you want to import, manufacture, or deal in NFA items - then it's an annual tax of either $500 or $1000 on top of your normal FFL fees.)