I've had quite a few teachers in college who just read from powerpoints and now I know why I get bored.
Basically, if I understand it correctly, your brain can't handle getting the same information at the same time from hearing and visual cues. So if a slide said "Monkeys are animals" and the presenter says "Monkeys are animals," your brain gets confused. Okay, that's probably an oversimplification, but it should get the point across. Powerpoint isn't the only cause, it's any slide presentation app, or actually anything that has visual and audio cues saying the same thing.