I know there's a huge swath of "promotional consideration" names at the end of a lot of shows now, so that might be where they dump a bunch of that stuff?

I think the difference is that celebrities and "influencers" are real (-ish) people, so if they say they recommend something, that's an actual piece of anecdotal data when deciding whether or not you want to buy into it yourself. If somebody in a movie says they're going to Fyre Festival, that might loosely associate the thing in your mind with "coolness" or whatever, but you're not going to mistake it for an actual endorsement from a real person.

I think the law actually states that media that is meant to be shown in a theater is exempt. I guess as to not take away from the experience of watching the movie.

Movies are fictional.

If a celebrity is giving an endorsement in a scripted movie I'm obviously going to think of the endorsement differently if theyre giving it in an Instagram post. That's where the FTC says "hey, you have to be clear you are benefiting from this advertisement" because otherwise (in a movie) it would be clear the endorsement isn't personal or organic.

Also not all of what you may call "product placements" in movies is paid. For one example, the red Swingline stapler in Office Space wasn't a paid product placement nor did Swingline even make a red version, it was a product invented for the movie, Mike Judge had an auto body shop do a paint job on a black stapler. Yet the movie created a market for red Swingline staplers, Swingline started producing red staplers, and it became their best selling product.