Customize how? It's a bit difficult as, with syncing to Clients, having default names makes that integration more accessible for the vast majority of users. Sure, some clients (most, maybe?) allow you to specify which folder syncs to what, but I'd bet the vast majority of people don't know about that functionality. So while it is possible to sync, say, a "New Mail" folder to "Inbox" in eM Client, not everyone knows you can do that so it would make more work for people supporting end users.