The choice of puppies is weird but a snakes gotta eat and you can't exactly just feed them a head of lettuce. Is puppies really that much worse than piglets or rabbits?

Once a snake gets to a certain size rats won't be enough anymore. At that size there aren't any good mass market options so those snake owners will usually take what they can get. I knew a guy that bred reticulated pythons and he wound up having a deal with a pig farm where they would sell him any piglets that happened to die early for dirt cheap (because what else where they going to do with them). But if you don't luck into an arrangement like that what do you do? If you have an ample supply of unwanted puppies I guess it would make sense to use puppies. As awful it sounds to western sensibilities, dogs are livestock in other parts of the world.