Critics came down quite hard on Seth MacFarlane after what I thought was actually a good job hosting the ceremonies. First off, this isn't the Golden Globes where everybody in attendance has an everlasting flow of alcohol being refilled at their table. Second, the critics are undeniably harsh and merciless when it comes to critiquing Oscar hosts.
So when Tina Fey was unofficially asked to host next year, she said "nope."
The Academy is going to have a tough time finding a new host. Good luck Academy!