"how come some states have magazine restrictions?"
because they don't believe what the Constitution states nor what the Founders believed and gave us!
The left is not about personal consequence or accountability's. Its about control and feel good vibes.
The mag limit protects no one and endangers many. Those who would observe the limit will be victimized by those who don't. A home invader cares nothing about whether or not his magazine capacity is within legal limits and neither do his partners in crime. The law abiding citizen is forced to defend himself with one hand tied behind his back. This is the reality of all gun control.
The reality of any form of gun control is to eliminate them completely. Magazines, buying ammo, differ stocks, waiting periods, red flag laws, gun manufacturers, background checks, taxes, etc., etc. It is all designed to get your guns and prevent you from owning them.