I have a working theory that character design works on one of those triangle graphs with three poles, and a strong design either lands strongly towards one pole or hits a good mix of two. And while what the three are can vary by medium and genre, for a video game RPG we're working with Sexy, Badass, and Cute.
Githyanki are none of the above, so they're the least popular. Gnomes and Halflings are pushing the Cute axis. Dragonborn, Half-Orcs, and maybe Dwarves are all primarily on the Badass axis. And Elves and Drow and Tieflings are all leaning on the Sexy axis. It should be obvious what how the three axis rank in popularity.