Off the top of my head, podcast transcripts are good because they:
— Are Important for accessibility.
— Are required for your podcast to be used in a classroom.
— Can help you get more exposure if people find them through search.
— Can make your content easier to share. (If you have a friend you know won't listen to a podcast, you can still send the info.)
— Provide an entry point for people who aren't ready to commit to listening.
What else?