The current audience for Lemmy/Fediverse is a niche group. This group highly prefers linux. It cares (and knows about) federation. It cares about adblocking. It highly prefers political discussions. It cares about privacy.
But it's not, actually. The instances you choose tend to federate with similar instances while the instances for the people who are not like that, are just not shown to us as a group. And I'm perfectly fine with that. Does it make Lemmy a bubble to some degree...sure. And are the vast majority of instances exactly as you describe...yes, I'm not denying that.
But outside of our circle of instances, there are hundreds of little instances that are just for themselves; their family groups, their workplaces, their DnD Campaign, etc... We don't see them because we aren't federated with them, but that doesn't mean they don't exist.
Lemmy is more than just where we sit, typing away at each other. Lemmy is the technology itself, and it's used in far more places than just our little bubble of politically minded privacy respecting tech nerds.
Edited: Heck, I'd be willing to be you that somewhere out there right now, there is a dark-universe Lemmy made up of all the Nazi, right-wing instances that federate with each other, and we would just never see them in our feeds because that's the beautiful thing about federation/defederation.
Even the stupidest person on earth gets one right every once in a while.