Why do courts consider legislative enactments, restrictions on the right to arms, as evidence of the popular understanding of the Second Amendment? Those seem to be the main focus in recent decisions.
The underlying reasoning must go like this: (1) legislators would not enact a law if they thought it was unconstitutional (yeah, I know this is quite an assumption) so (2) the fact that they did enact a restriction on a right (around the time of the framing(s)) is evidence, or at least suggestive, that what was restricted was not seen as within the right in question.
Apply that to the Second Amendment. As of Barron v. Baltimore (1833), the Supreme Court had ruled that the federal Bill of Rights did not restrict the states. As of the Slaughterhouse Cases and Cruikshank (1873 and 1876), the Supreme Court had ruled that the 14th Amendment didn’t require states to conform to the federal Bill of Rights, either.
So state legislatures would have understood, throughout the 19th and 20th centuries, that the Second Amendment did not bind them. The above reasoning is thus without basis. A state legislature’s enactments don’t suggest that the legislators thought the restrictions comparable with the Second Amendment, because they wouldn’t have thought that the Second Amendment constrained their actions.