Well, thanks for a lesson on the laws that banned these weapons. But that doesn't answer the question, which is why those particular weapons are banned (you did indeed answer this about early machine guns, but that isn't relevant to later bans because Bonnie and Clyde were, you know, kinda dead).
Why were those weapons banned, but not handguns, shotguns, and semi-automatic rifles? What are the substantial differences between these groups of weapons that causes one group to be banned and the other legal?
Well I was slightly wrong. In 1934 I believe they just needed a tax stamp but the tax was $200 a year in 1934 which was prohibitively expensive. By 1986 there were very few people who owned these weapons.
The main reason is that very few people owned these weapons and they were therefore easy to ban or place restrictions on. There was no data regarding their lethality.