Because then JKR would have missed out on a chance to call one of her characters a bitch? (I like how when Molly kills her she doesn't actually DIE. Just um turns to dust or something? What even was that.)

It is a GIANT SNAKE not unlike the one her first boyfriend who happened to be the Dark Lord made her set on her schoolmates when she was ELEVEN. Also Bellatrix is the one who for all intents and purposes orphaned Neville. MAKES WAY MORE SENSE THAN THE ACTUAL ENDING, DAMMIT.

Yyyyeah. (Surprisingly few people seem to have picked up on that? But ew ew ew.)