Frozen is not only Disney's highest-grossing animated film, it's the highest-grossing animated film period (according to Wikipedia.)
But why? I really don't understand.
I think that the film is highly, highly overrated. Let's just compare it to Disney's second-highest-grossing film, The Lion King. (I'm not counting Pixar movies as "Disney", even if Disney currently technically speaking distributes them. Even then, only Toy Story 3 would be higher than The Lion King.)
The Lion King actually tells a profound, memorable story. It establishes characters well, and they are also likewise memorable. It's a well-written film overall. If somebody were to see the film for the first time, and then a few weeks later you would ask them to describe the story, and for details of what happened in the film, I'm certain that they could go to great lengths in their description.
Compare that to Frozen. If you did that same test, I'm all but certain that such person would only be able to describe but a small fraction, compared to how much they were able to describe The Lion King.
The premise is perhaps the only memorable thing about Frozen. There's this princess who is like a King Midas of freezing, as she freezes anything she touches and can't control it. And at some point she runs away because of that, and... well, not much really. That's about it. That's all I got from the film. A premise, and pretty much nothing else. In fact, not much happens in the film; nothing very memorable at least. There's that one song that got viral, but that's not really part of the story. I think there was some bad guy who wanted to kill this princess for some reason, or something, and... I can't even remember how it was resolved.
What I am trying to say with all this is that the film is extremely shallow. There is a somewhat interesting premise, and pretty much nothing more. There is no profound memorable storyarc, and nothing much to remember, or to be moved by, or get inspired, or anything. Most of the film feels like just padding which is quickly forgotten and doesn't really add anything.
Contrast that with The Lion King, which story could be quite well be described as epic. At the very least memorable. Perhaps even profound at some level.
So why is Frozen regarded so high? Why is it the highest-grossing animated film of all time, while animated films that are significantly better than it are not even nearly as popular? I don't get it. It's just highly overrated.