Because no PC power supply has a 24V rail and even though there's a fancy new connector you can still use an adapter to get the old-fashioned plugs.
After all you don't want to limit your market to people who can afford to buy both your most expensive GPU and a new power supply. In the PC market backwards compatibility is king.
After all you don't want to limit your market to people who can afford to buy both your most expensive GPU and a new power supply. In the PC market backwards compatibility is king.