What do you mean? None of the extra charge is going to the workers. Amazon is simply taking a larger cut of every transaction. If anything, this may put downwards pressure on worker wages as employers pass on this new fee increase to their workers.
As a semi-regular user of MTurk, I find this new pricing excessive. Most products grow its revenues by acquiring more users instead of jacking up the pricing. I don't understand why Amazon needs MTurk bootstrap its new features growth. Surely, this is a relatively small team compared to Amazon's main products?