Maybe there was some reliability guarantee or it is just a tiny government office will little technical background.

The leasing model (it's not 100% certain from the article that they have been leased) may make sense for disks, if the idea is that after some time they must be necessarily replaced.

Assuming they were leased, since the client returned them (instead of purchasing them), physicial space may have been a reason.

Wouldn't it mean that the lessor would be allowed to sell the drives? I mean if you rent them out, and they are handing the goods back would you just destroy them? Something doesn't sound right here.

Well recycling heavily used disk drives sounds more like waste disposal, I mean who can you sell that shit and get away with it? Maybe give em away if they work, idk.