Political expedience. The overnight switch furthers the extension of governmental control on a worldwide basis. The billions of years are a moving goalpost routinely pushed back to allow sufficient time for presumed random mutations to occur. The randomness reduces humanity to a beast and removes God from the equation.
Science has become so thoroughly political that it's starting to sound like Lysenkoism under the USSR.
Yes, it is. I just read a book about a Jewish family in the USSR, The Gates of November by Chaim Potok. It mentioned that entire faculties of biology were dismissed from their jobs because they disagreed with Lysenko.