If the Vita would have blasted off into space and killed all 3DS sales, the Vita fans would all be marching 'round the campfire hootin' and hollerin' about how the Vita crushed the 3DS - and they would have let everyone know it, too.
But the reverse happened - the 3DS crushed the Vita. It's not that Sony botched the launch or did something wrong, it's that consumers are allocating their money to the 3DS INSTEAD of the Vita.
The poor Vita sales are a SYMPTOM of a larger problem for Sony - consumers are buying SOMETHING ELSE.