Doesn’t that say they default new users to a server owned by them? That’s the same kind of thing as defaulting to Lemmy.world for Lemmy apps.
What I mean is a larger list of trusted instances. Including ones outside the control of one organisation, though I get that this is risky for Mastodon because they don’t want to default people to somewhere that’s going to shut down or have some drama and ruin a hard earned brand.
We probably have more leeway to do it in Lemmy apps since (with the exception of Jerboa) they aren’t developed by “Lemmy”, and Lemmy.world is also not run by “Lemmy”. But for this same reason, " Lemmy" has no control over what these apps default to.