Think about the last time you really learned something and specifically, how did you learn it? Was it via PowerPoint? No? Maybe you Googled it, read about it in a book/online or asked someone and got a good explanation? Maybe you even did the dance of trial/fail until you trial/succeeded?
If you don’t learn via PowerPoint – why do you think we often choose PowerPoint as our number one instrument to teach? Even though this question was rhetorical there actually is an answer:
Because we want to make everything clear, concise and easy to understand.