* more expensive
* amenable to more gear of various kinds ("tactical")
* the ammo is much more expensive, and much easier to fire quickly
* used more among enthusiasts, a.k.a. "influencers"
So basically, you sell a pistol to someone, get a $500 sale in a competitive market (probably low margins), and sell some ammo and range time a few times a year.
But if you sell the tactical stuff (e.g. assault rifles and other gear-accomodating stuff), you are likely to get a few high-margin follow up sales and a more enthusiastic customer who might involve their friends, use more ammo, etc.
There are casual gun control proponents who likely don't know this about the gun industry.
There is another, much smaller, but potentially more effective, cohort that very much do. I've read literature from and spoken to activists that very much are attacking assault weapons strategically. Both because of them being an easier target, especially after a mass shooting, and because of the revenue implications.