If you have fifty nodes, you don't want all fifty working on every database. Each db should only be associated with with nodes to have a healthy quorum. But this is fine: you probably only have 3-5 regions. Each region could have 1-2 nodes supporting each db. It's almost certainly the case that you don't have dozens of regions/PoPs (and if you do, the material difference in latency between one PoP and another is probably ones of milliseconds for most users).