That’s because there aren’t any. Inside a series recording folder the oldest are the top of the list. When you look at the recordings list which of the many possible recordings within a series recording list do you want to sort on. ? The list is sorted by the folder containing the last recorded series folder with a new episode.
If you open the folder the recordings of the series are in the order you want. Most however want it to be the other way round.
Should be a user sort order option.