Maybe I’m not getting something here, but neither Mastodon nor Lemmy are private, you can find everything open for everyone already, so how would federation change something there? Federation doesn’t mean everyone would use their app, so they wouldn’t gain any app usage analytics.
Also I don’t get how your metaphor make sense. The amount of fediverse users is a rounding error next to threads, instagram, WhatsApp and facebook. So there’s not a “lot a tiny things that can add up”, only a small amount of tiny things which don’t really add up to anything.