The difference is the "algorithmic" timeline (meaning ads) you get with Facebook, Insta, and co compared to the strictly chronological timeline you get on the Fediverse equivalents (Mastodon, Pixelfed). That it's less addictive, or at least not in the doom scrolling type of way, is more a consequence. Aka the enshitification argument.

Masto specifically is also a Twitter not Facebook replacement, with everyone soliloquizing past each other rather than holding a genuine conversation.

For the actual "good" Facebook use cases such as keeping in contact with school/uni veterans or other closed group, there's friendica, but it's nowhere near Fb in terms of volume.