Except for the fact that this doesn't put any pressure on anyone who wants a gun (those are still really easy to get in California, just not as easy as most other states). But those who benefit the most from this law are gun manufacturers, and not long after when this bill is extended to printing replacement parts for anything, all companies that charge inflated prices for repair parts or design their products to be unrepairable entirely.

What people who print "guns" are actually printing is gun furniture. Custom grips and the like, either for comfort/aesthetics or so they can take cheaper gun parts and use them to build a clone of a similar gun from a company that charges more. They still use legally purchased gun internals.

The gun that Luigi Mangione supposedly used was a Glock, legally purchased and one of the most ubiquitous pistols in the world, with a 3d printed grip on it. Every other part of that gun came from the manufacturer.

The gun used to kill Shinzo Abe, however, was made entirely out of simple materials readily available at any hardware store and is completely legal in all 50 states. Because a gun like that is considered a "garage gun" and those are legal under federal law because it's essentially impossible to stop somebody from gluing together a pipe and a nail to strike the bullet with and fire it down the pipe barrel. But 3d printed gun parts don't fall under the same regulations and those who stand to lose the most from people 3d printing are those who charge unreasonable prices.

You know who else would benefit from this law? Games Workshop, who sells many miniature figures for $40+ each, and a few for over one thousand dollars.