I dunno ;_; it must be some misguided sense of "it looks cuter"... when my sister's boyfriend brought her as a little pup, her tail was already chopped, and worse, they hadn't even treated it! My sister had no idea, and only noticed when poor little Pituca started to walk funny and have trouble moving her hind legs. Sis then had to apply antibiotics on her little stump twice a day, and it looked painful ;____; But now she's healthy and almost an year old!
She's not very enthusiastic as of late, since her "mama" (my sister) is traveling and she misses her :< on the first day, she'd paw at the doors until someone opened them, then she'd sniff at the insides and sit back going all "my person is not here! where is my person?". She's better as of late, but I imagine when my sister comes back she's going to become an unstoppable whirlwind of hyperness.