Why is lever action better for rifles and pump action better for shotguns?

Answer 1

They are both lever actions, in a way. It's a question of mechanics. Lever action rifles fell out of favor for a variety of reasons. Difficult to fire prone (lever travel), tubular magazines (blunt lead bullets only), loss of sight picture, I'm sure people can add their favorite. Pump actions weren't very popular for rifles for many of the same reasons. Tubular magazines aren't hazardous for shotguns because of the wide, blunt, plastic ends don't pose much hazard of igniting the round in front of it. The best shotguns in the world, and the best rifles for that matter, aren't lever action or pump, they are bolt or dual barrel.

For firepower - Semi-auto gas or recoil w/ spring return

For accuracy - Bolt/break action

For a civilian compromise - lever action/pump

I've fired both. For a shotgun, fired at an angle from a standing position, the pump is more ergonomic than the lever. For a rifle, standing on a more horizontal plane, it comes down to preference.