I use MP3 because it works on just about everything I own. Nothing is more annoying than when you have nicely prepared a USB stick with travel music and in the car nothing works and the computer is 500 km away.

This is why most people bother with MP3 still, we don't care that there is something more recent. Or rather, we do care but have no use for it yet. Not always is the new thing better than the old for your use case.