The Khajiits from Morrowind on have always been Suthay-Rahts. They can't put all the Khajiit races in Skyrim because that would be tremendously unbalanced and a nightmare to do. Imagine how more complex the game would be if you got gigantic tiger cats running around or house cats that are actually Khajiits.
I think the reason why Bethesda chose Suthay-Rahts was because they are they are probably the most balanced Khajiit subspecies that isn't overpowered or under-powered and wouldn't present ingame issues such as being too large to fit in a doorway.
Same could be said with the Argonians. Imagine how scary it be playing as a Naga.