They think people will pay more for an e-book than they will print copies — and let's be honest, the $ 14.99 for this e-book is more than we'd pay for the mmpb version.
Additionally (and it may be a French specificity), the publisher which has rights for the «trade paperback version» (and the ebook), resells the rights for the MMPB to a secondary publisher (sometimes in the same publishing group, but not always).