How to reproduce:
Fly high up in the sky in creative mode
You'll see that when you hit the ground no sound plays.
If you toggle falldamage false in the gamerules and switch to survival mode while you're high in the air, you'll see that the sound plays when you hit the ground.
MC-161120 Falling from a height in Creative mode plays no sound when hitting the ground but in survival with fallDamage turned off it does