Because it’s in fashion – with good reason! The number of people listening to podcasts has exploded in recent years, and there is every reason to think it will continue.
Besides how sympathy and depth are more readily available in podcasts than through written media, it also allows reaching out to a very specific demographic in a direct, engaging way.
As a podcast listener, you have the advantage that other things can be done while listening – e.g. during commute, which makes it significantly more flexible than video or text. Add to that, producing podcasts is significantly cheaper than e.g. producing videos.