On the basic end: because they’re cheaper, use less energy, are more reliable, and last longer.
On the fancy end: have you seen demonstrations of Audi’s matrix LEDs? They have the ability to dim specific areas dynamically, so that they can track incoming traffic and keep them in a dim-zone while still keeping the road and shoulders well lit.
Keep in mind that there is nothing special about LEDs that make them brighter; they can make LEDs dimmer and they can make halogens brighter, but the manufacturer has chosen not to.
On the basic end: because they’re cheaper, use less energy, are more reliable, and last longer.
On the fancy end: have you seen demonstrations of Audi’s matrix LEDs? They have the ability to dim specific areas dynamically, so that they can track incoming traffic and keep them in a dim-zone while still keeping the road and shoulders well lit.
Keep in mind that there is nothing special about LEDs that make them brighter; they can make LEDs dimmer and they can make halogens brighter, but the manufacturer has chosen not to.