Because you’ve never flown extended over water (I mean longer over the water than our longest flights in total currently at NK) or a part of the world where HF is really poor quality and the frequency is overcrowded and heavily accented.

Oceanic clearances, altitude changes, weather deviations, pre-armed auto position reports, emergency and urgent situation updates, it’s a clear and concise communication tool.

Flying over the congested airspace in Europe, CPDLC log on has been optional, and they have excellent VHF like in the US. Why bother with it you ask? Never worry about losing a frequency again, and nearly every time I logged on I was given direct routing across Europe. You also have a printable record of all ATC clearances, and a visual confirmation of things like altitudes and frequencies.