Why does any company's product launch fail? Arrogance, intellectual laziness, chasing a trend off a cliff. Same way company owners sometimes check out and hand over the reins to management consultants.

I am not privy to their sales data; perhaps it looks terrible and they panicked. While there has been a big backlash, I don't think adult nostalgia is as profitable as childhood enthusiasm; parents might buy Roald Dahl for their kids, but there are plenty of other authors competing for their attention.