Not “reserved”, it’s just what most customer want.
Pump action rifles are available, but they’re not very popular. A pump action allows a fast, two-handed, follow up shot, allowing the shooter to maintain eye contact with the target (clay targets, pheasants, rabbits, etc.). It’s also easier to keep the shotgun butt in contact with your shoulder, and the comb in contact with your cheek. That’s usually not necessary with a centerfire rifle.
Shotshells also produces a lot less pressure than centerfire cartridges. While a shotgun requires a strong, solid, reliable, locking action in order to repeatedly send an ounce+ of lead pellets downrange, the pressure created by more powerful centerfire cartridges would destroy an action designed to only handle shotshell pressures.
It also depends on which type of action you are used to. For decades, my dad hunted with a Remington Gamemaster, Model 141, pump action, takedown rifle in .35 Remington caliber. He also preferred pump action shotguns. I never liked pump action shotguns, or rifles. Just never felt right. To each their own.
Bolt action shotguns are difficult to cycle quickly while keeping your face on the stock, and the butt on your shoulder.