Ask HN: Why can't kindles “nest” data structures?

Kindle has released an ability to collect a series. But, this is a list/set structure which displays "alongside" the collections model. E.g. if I have Asimov's foundation series filed in SF as a collection, I see 3 discrete books inside SF/ and I see one "series" structure of 3 books outside the collection.

Kindle post dates every OS i know having nested logical structure for file like items. Directories can contain directories. If you USB mount a Kindle FS its obvious it has directories. The UI however maps collections and series differently from some other model, not the filestore.

Can somebody explain to me why the Kindle abstraction over information cannot handle nested structure?

(To me, series but not inside collections is just designed to make me angry)

Obviously it's feedback I'm giving Amazon directly, which typically, is ignored.

I'm kind of seeking clue in the computer science domain why this fundamental concept wasn't "baked in" to what kindles do.