My guess: They were created expecting an in rush of users and content from R/ but when that didn't happen, they got bored and moved on.
There are many, many, r/sub clones that were created during the API shit. The people creating the subs had no intention of creating content, they just wanted to be a mod. Now they lie as empty as the day they were created.
I don't know how many other people had the same thought, but I thought about snagging a couple community names, not because I have any interest in being a mod (I really don't at all,) but to hold onto them until either former reddit mods showed up or at least someone else who seemed like they had real interest in actually running the place and didn't seem to be an opportunistic power-tripping asshole who would run it into the ground.
I didn't end up doing it, but I gave it some serious consideration.
Well there were some communities I was happy to see cloned on reddit like privacyguides and Android. Would have been happy to see bunch of other communities I had enjoyed enough to subscribe on reddit to have moved over here.