[linsomniac]

The "recommended songs" playlists seem to have more diversity, but also seem to be fairly short (they'll repeat in a couple hours it feels like; I rarely listen to them when I'm working because they'll start repeating, and I don't usually listen to music for a large fraction of the day, so I'm guessing 1-2 hours).

My best guess is that they are assuming no playlist is more than 50-100 songs, and are limiting the shuffle to that number, so that a shuffle doesn't consume too many resources (memory, database hits, CPU cycles). Maybe someone, possibly in the distant past had a large playlist that caused service problems. And because of that they clamped WAY down to prevent it.