Because it’s AMAZING, that’s y.
For me personally, I think TLK is so popular because it truly touches you and moves you in a way very few Disney movies do. It’s just so majestic and powerful, a true masterpiece.
The very core of the story is responsibility, and about how you cannot run away from your past and avoid conflict. You have to stand up and take responsibility for yourself and others. I think this is something everyone can relate to in some way.
Every person can see some part of themselves in the TLK characters and relate to their problems.