I’m not sure why you think that means the market for realistic prop guns is worth the cost of redesign and recalibration and possibly the purchase of new equipment.
Only a few companies make those movies, so they only need a limited stock of those weapons, especially since they can be reused. Most movies don’t require them.
Also, I can find absolutely nothing to corroborate your claim that movies were America’s biggest export in the 1980s. They aren’t even in the top 10 now, so I doubt it.