Earlier quoted context omitted.
I'm taking a guess at what the OP meant, but people focus on assault rifles and high-capacity magazines. Supposedly most incidents and deaths are caused by handguns. They're more affordable, and easy to discretely keep on your person. A data-driven policy would focus on them first, but it's easier to rile up the public about AR-15s so we keep doing the less-effective thing.
One might wonder about why ceramic plates are controlled in Connecticut or New York.
https://en.wikipedia.org/wiki/North_Hollywood_shootout#Weapo...
It's hard to find 1998 news articles about it now, but I would guess that the law was a reaction to this high profile crime.