"It's odd to me that HID headlights are so popular now, since they're such an old technology"
Essentially it's an update on the old carbon arc lamp, correct? That that technology has been around since what, the middle 1800s?
No idea. The ones used in headlights are, I assume, metal halide, which has been the most common type of lighting for parking lots, stadiums, and high-ceiling warehouses and garages, since they replaced high-pressure sodium and mercury vapor lights a while back. Of course, LEDs are cutting into that action pretty quickly.