Why is that particularly surprising? If the planes were certified with a particular landing light, it's an awful lot of paperwork and STCs to change things out. Plus, you wouldn't just be swapping out the bulb - you'd have to swap out the entire reflector to keep the beam pattern sane. The retrofit LEDs on car headlights regularly demonstrate what happens when you change from a more or less point source of light on the central axis (the filament in an H4 bulb or some other similar type) to a source that's "not that," you get all sorts of weird focus and cutoff issues.
Also, consider icing conditions. Any modern airliner is rated for flight into known icing, which includes deicing equipment. A halogen landing light is self-deicing for the most part (airliner landing lights are hundreds of watts, some are closer to a thousand). It will happily keep ice buildup away from the lens, whereas a LED will need some other variety of deicing to keep it clear. This is one of the reasons I use halogen bulbs in my motorcycle - I ride year round, to include in ice and snow (Ural, so has a sidecar, I can drive the sidecar wheel too, it's totally fine in these conditions). A halogen bulb keeps the headlight nicely free of ice buildup. LEDs don't put out enough heat to solve that problem, and it doesn't take that much ice buildup to totally scramble the beam pattern off a good glass lens.
You can get LED retrofit landing lights for smaller planes, and the club I fly with has them - but they're also Cessnas not rated for flight into known icing, so "keeping ice off the landing lights" is not a particular design concern.
Anyway, it surprises me none that airliners are still using halogens for the most part.
Also, consider icing conditions. Any modern airliner is rated for flight into known icing, which includes deicing equipment. A halogen landing light is self-deicing for the most part (airliner landing lights are hundreds of watts, some are closer to a thousand). It will happily keep ice buildup away from the lens, whereas a LED will need some other variety of deicing to keep it clear. This is one of the reasons I use halogen bulbs in my motorcycle - I ride year round, to include in ice and snow (Ural, so has a sidecar, I can drive the sidecar wheel too, it's totally fine in these conditions). A halogen bulb keeps the headlight nicely free of ice buildup. LEDs don't put out enough heat to solve that problem, and it doesn't take that much ice buildup to totally scramble the beam pattern off a good glass lens.
You can get LED retrofit landing lights for smaller planes, and the club I fly with has them - but they're also Cessnas not rated for flight into known icing, so "keeping ice off the landing lights" is not a particular design concern.
Anyway, it surprises me none that airliners are still using halogens for the most part.