In practice you’re most likely to be collaborating with other folks on your school project group, work team, close family, etc. Sure there are exceptions, but generally speaking picking a service location near your first group member ensures low latency for them (and they’re probably most engaged), and is likely to have lowish latency for everyone else.
On the flip side, picking US-East-1 gives okayish latency to folks near that, and nobody else.
And the corollary to that is that often your collaborations have a naturally low scale. While your entire app/customerbase as a whole needs to handle thousands of requests per second or more, one document/shard may only need to handle a handful of people.
On the flip side, picking US-East-1 gives okayish latency to folks near that, and nobody else.