MA isn't the only one to blame for this nonsense... applying the definition of "large capacity ammunition feeding devices" to belts as well as magazines, was part of the 1994 AWB. Ammo vendors in those days would break up the belts (if disintegrating), into 10 rd sections, repack them in the ammo can, and sell them that way.
MA just chose to continue the nonsense after the federal ban expired.
The law also mandated the "LCAFD's" have markings to show date of manufacture.
In order to meet that requirement, the ATF required ammo manufacturers to label the boxes/cans the ammo was shipped in and not individual links... meaning, about the only way someone could be busted for illegal possession was if they didn't de-link the stuff and kept it in it's original factory packaging.