I came here to say the same thing. This move probably has everything to do with making sure people don't have to constantly change the volume when shifting between music videos and random amateur cat videos. The simple fact is YouTube can't change the average loudness of a given audio track without applying some form of 'destructive' processing, either compression or expansion. A more dynamic track will always be on average, quieter than a less dynamic track. Re-processing a bunch of audio tracks with just normalization does not change their average loudness, unless of course they are selectively applying compression to audio they find in need of a boost.