The way they are implemented is certainly a bit odd.
It is until you think of the GUI from a coders/presentation perspective.
If you do it 'properly' then for elves (and *only* elves) you would have:
-Race
-Subrace
-Sub-Subrace
Alternatively, you have:
-Race
-Drow 1, Drow 2.
ALTERNATIVELY STILL you would have:
-Race
-Subrace
and then somewhere else "Not evil drow" because you need the code flags to be seen for dialogue options. It can't be the relegion flag, because that doesn't exist for anyone but clerics Unless you remove the different flags, and allow you to be an evil drow pretending to be a good drow or vice versa, but that in turn can potentially put strain on writing, especially if you keep doing 'opposite choices' repeatedly.
All of this is more 'unique' coding, more chance for bugs, which means more testing and more potential code-goblins.
----
*Or* you make drow a 'seperate' race (feeding into one of the creation myths of Drow, and how they've become very different to other elves thematically) and make the different 'types' subraces, allowing a quick, clear display that also follows the structure of other race choices, avoiding potential confusion.
edit: as an aside, I honestly think this is why female characters can have beards when their male counterparts can. It's one less bit of code to put in and bug, and who cares if you want a bearded lady anyway?
