Thats because it's not, the second stands on it's own and incorporation by the 14th is neither necessary nor desirable.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Massachustees is infringing, not regualting. Good case for SCOTUS when Alito gets there.
The good news is the Congress will not go there. Lott made a huge difference, in changing the terms of debate on gun control. It sucked the oxygen out of the "gun grabbers" on th issue. Ideas backed with data matter, they really do, in this case that an armed society really does seem to engender a polite society, based on the data. It changed my view. But Mass as I said wants to make a cultural statement. It gives meaning to the state of being of being a New England activist. It is in the genes of the place, which genes somehow managed to be passed on from the Puritan Calvinists to the Catholics. The Yankees in New England won, even while losing out demographically. Which reminds us, that it isn't all about demographics either.