Our constitution has that wonderful bill of RIGHTS.
No other country on the planet would even think of allowing a citizen to to have a collection like his, because they don't have the right to own guns as part of the basic laws governing how the government can operate.
If is not just because we wants to, it is because he has the the RIGHTS to do so. He likely personally owns more weapons than the entire country of Australia and Great Brittan combined outside of the military.
If you had the money can you own fully automatic 50 cal Ma Deuce, and a couple of operational tanks?
Only because he has the right to, he does.