it’s true that it doesn’t particulary increase the distribution of your post but the idea that we’re all here to get things distributed as far as possible is pretty weird
the funny thing about this: on the Pleroma/Misskey side of the network, favorites distribute posts across servers the same way boosts or replies do, they just don’t push the posts directly to followers’ Home Timelines — so they do increase distribution, but in a less obvious way (it’s more obvious on smaller servers like mine where any interaction could facilitate federation that would otherwise would not happen).
it doesn’t really work that exact way on Mastodon though from what i’ve seen, as Mastodon doesn’t seem to federate favorites at all except to the post author.