In Medieval Europe, several countries banned crossbows and arbalests for civilian use. The reason was transparent: protecting the monopoly of armored knights and soldiers on effective violence. Crossbows were far easier to learn than longbows and quite effective against armor at close to medium range. In our days, crossbows are still banned in quite a few places.
American government hasn’t banned the modern equivalent of the crossbow, the rifle, yet. But they did quietly ban bullets that are relatively effective against armor last year. Used primarily for dangerous game hunting, lathed brass bullets are no longer legal for civilian ownership. Even the hollow point bullets designed for controlled expansion such as shown above are considered AP based on the alloy used.
You can see the result of having only low-penetration ammunition available: most American rifles won’t defeat cover effectively. They can still penetrate soft vests but not even the wimpiest of the hard plates. In the video, the only good penetrator ends up being imported 5.45×39, mainly thanks to the relatively thick jacket. But .308 bullets available today are much less effective against cover, vehicles and armor than WW2 vintage 30-06 AP ammunition was. In combat, that puts American civilians at an added disadvantage relative to the various enforcement agencies who have armor and aren’t so handicapped in the choice of munitions.