The devs have cited server latency as the biggest reason why they're unwilling to add more customization options. Essentially, each new slider that you add to character creation is one additional value that needs to be piped from the servers to every character that sees your character in game, so that your character can be properly drawn on their screen. Then you multiply that load by the number of characters you see on screen at one time. Even just one additional slider results in a massive boost in the amount of data being sent out at a time.

As a matter of perspective, the devs were similarly concerned about adjusting inventory size - and unlike the potentially hundreds of people who can see your character, only ONE person can see your inventory: You. They're grudgingly giving us a few more inventory slots, but I think it'll be a long, long time before they give us any additional values to play with on our character's appearance.