I don't generally stretch one encounter of a couple of paragraphs into an entire session.
And, really, the bigger challenge is not in preparing for individual sessions, it's in knowing the adventure well enough before starting the adventure in the first place. That's the big time investment that becomes challenging.
I get that some people really enjoy reading long-form RPG supplements. I do. I used to be like that. And I'm sorry if there is high-quality content you don't enjoy because it's presented in a more terse, powerpoint-like format. But it's what makes some of us willing to, for example, say "yes" when our kid's D&D group at school asks if you'll start DMing for them.
Yeah, making sure the hobby is only accessible to those who are able/willing to devote hours to long-form reading (much of it terribly written). That should really keep the industry thriving.