Revisit: iCloud Selective Sync

I'm still very puzzled as to why a selective sync option isn't available with iCloud. Basically the most prevalent explanation is that iCloud is not an archival service, it's a syncing service. OK, then why do we need to buy all that STORAGE space? If it is merely syncing one device with another then all that is needed is some amount of buffer space for transfer of syncing items, and maybe a little more for things like storage of backups. And if it's for backups, then why does the backed up information from one computer need to get downloaded to another computer. Such an explanation also doesn't address the problem where someone uses one computer for working on large amounts of files that they want backed up, but they don't work on them on another computer that gets bloated up and forcing iCloud to manage disk usage of an over-full disk all because a large amount of unneeded stuff got downloaded. For example, I work on a large collection of photos on my iMac and I don't need any of that on my MacBook Air, but it still tries to download 1TB of data. All because a simple option to not sycn certain folders isn't provided. This just doesn't make sense.

Does anyone know of any work around? Even if it takes some complicated command-line set up in Terminal.