The way I look at it is that levels only make sense within an organization that is big enough that a hierarchy is needed to scale. At that point staff+ IC levels are needed because you want purely technical people on the same pay scale and influence level as managers to counteract the incentives of empire building that can corrupt the entire architecture and lead to a Dead Sea effect of engineering talent if left unchecked.
From this perspective most staff+ work is in some way generating influence and impact across multiple teams and individuals. Outside of certain specialties and specific R&D roles I think it’s pretty hard to justify staff leveling on purely technical work.
Of course different companies calibrate levels differently, and they’re all subject to level inflation, but that’s my feeling for a traditional Google L6.