The telemark turn is more stable than other methods, particularly in soft snow, when your boots aren't attached at the back, which is necessary for efficient movement on flat and uphill areas. The introduction of lifts opened up exploration of specialized equipment just for descending, leading to the fixed alpine boot and popularity of the parallel turn.

Of course, since it predates modern carving skis for alpine skiing ;)

I can't imagine skiing with stiff carving boots in the age before the ski lift.