This is a weakness of ad-supported business models. When users are buying or subscribing to a product, you want them to love it as much as possible so that they will always buy more. Ad-supported models untie the relationship between UX and revenue. In an ad-supported model, you do need users to like the product enough to keep coming back, but small decreases in utility that generate more impressions could be great for revenue.

The people at Facebook are extremely talented. It's a shame they're stuck with this business model. It would be awesome to see how good they could make Facebook if this wasn't tying them down.