Because they will be found unconstitutional if challenged; the finesse is in getting the laws to stay on the books to have what effect they can, and to appease the voters who support those laws, while avoiding enforcement situations that would result in a direct challenge. It's the cat and mouse game that goes on between the branches of government.
Also see why some gun laws are written in an extremely obfuscated and convoluted manner, for example the law that became a point of contention in State v. Rittenhouse.