The core devs have always been pretty open about how they don't want lemmy.ml to be "the flagship instance". To them, it's just the instance that they run, and so happens to have the history of being the biggest instance back when lemmy was growing its user base.
They actively encouraged new/other instances be created and pushed new users during the reddit migration to other instances, rarely listing their own instance in the list of recommended instances on join-lemmy.
So it's not the flagship, and intentionally so. And while lemmy.world is the biggest by far, it is also arguably not the flagship either due to the lack of having the core devs or contributors as admins of that instance. All of which means lemmy has done something most other platforms have struggled with (I'm looking at you mastodon.social!), which is flattening the power structure amongst the devs and admins such that there is no real flagship, an all around good thing IMO.