Q: why is it so hard to actively listen to the harmonies? it's super easy to hum the main melody but I have a hard time even making out harmonies that aren't in relatively quiet and small chunks, let alone humming them.
A: usually the harmonies are quieter. the part that is supposed to enter your brain is the main line. if you spend some time playing piano/keyboard, you'll start to understand what's going on, and then you'll be able to find harmony parts in your mind by imagining the chord formations on the keyboard