They'll eventually want to set it up so you read the sponsored content first, before seeing the tag saying it's an ad. You're more likely to absorb it then.

Especially if it's LLM-generated to fit with the context, the message will slip right into the mind. Then a little "(Sponsored)" at the bottom after you've already consumed the ad.

This is a bit like how ads are presented on X, they look like regular posts or replies but they usually feel off topic and you're thinking "huh, this doesn't fit the discussion". But LLMs will allow much more seamless and sneaky ads.