I think the reason they mention the timeline is because it's great for advertisers. It doesn't seem unlikely that it has intentionally been designed to be disor

I think the reason they mention the timeline is because it's great for advertisers. It doesn't seem unlikely that it has intentionally been designed to be disorienting which leads us to pay more attention to ads. User retention (including engagement and growth) and monetization are obviously the two biggest concerns for a company like Facebook. Photos (sticky, long-living) and the map of users (if you are not in you are out) are for user retention. Timeline and platform (games, connect, pages etc) is for monetization.