Because they assumed that there was a good reason that their friend sent it!?
I had a friend who did the same to me, I was sent a message asking my opinion on a tech topic. I spent 30min researching/reading to make sure my reply was accurate and then found out the question was generated by a LLM, and he just wanted to show off how good a LLM was.
It will color every interaction you have with that person...
I think you are leaving the human out of the loop. When a friend of mine recommends me something I'll lower my skepticism because I'm assuming my friend would not send me garbage.
If a random podcaster says "I've proved that P=NP" I'd say "no you didn't", but if a math professor sends me that same link I'll keep listening to see where this goes. And I've definitely read texts making wild assertions that only at the end were revealed as hit pieces and/or propaganda.
Even if you think your friend would only send good things, you would realize that something is vomit in less than an hour. I cannot understand someone listening to something for an entire hour and then whining that they waste their entire hour and it was vomit, you're not in a cinema, you didn't pay a ticket for it, you listen to something because you like it or move on.
You can argue your point all day, it will not resolve their cognitive dissonance.
No matter how convincing, high-quality or entertaining it was, no matter for how long they happily consumed the content: it's AI-generated, they hate AI, therefore it's vomit, period.
I had a friend who did the same to me, I was sent a message asking my opinion on a tech topic. I spent 30min researching/reading to make sure my reply was accurate and then found out the question was generated by a LLM, and he just wanted to show off how good a LLM was.
It will color every interaction you have with that person...