Why does a pickle have bumps?
Bumps are where the thorns grow. Of course, stores typically powerwash them off. But, my market has them...and they are tiny little stings when you pick them up. ;)
Because otherwise they'd be so slippery you'd never get them out of the jar ;)
Because little cucumbers have bumps (from the prickles mentioned above). Larger cucumbers also have bumps, but, since there's more surface area on a larger cucumber, the bumps are easier to clean off because they take up a smaller percentage of the overall area of the cucumber.