I think if they were wide enough to get your arm down, there would be too much room for the crispies to shift around during transit, so more of them would be smitherined. A new verb, for you. Also there's the obvious point of a larger tube using more materials and being more expensive to mass-produce.
It would be no fun if the crisps were all smashed up, 'cause you wouldn't be able to shove two in your mouth and go "Ooh look, I'm a duck."
with nuts? a banana? am i missing something here? anyway, pringles tubes are perfectly gob shaped, allowing one to tip them directly in to the mouth, thereby avoiding irritating salty bits on your fingers.
I believe that 'thekraut' was comparing the Pringle tube with the proverbial sweetie jar in which the greedy monkey got it's hand stuck. Personally, when I get to the point in a new tube where I have to squeeze it in order to get my hand on the next Pringle I know it's time to stop :)