The term "fine" in "fine art" is not used to describe "better" art. Fine art is just a term that has since been abandoned for simply "art." However, some people refer to visual art, such as painting, as "fine art."
IMOP "better" art is art that pushes the medium and makes people who consume it think or feel differently than they did before they consumed it. The more derivative the work, the less impact it makes on both pushing the medium and on the way we think.
In order to change the way people think and feel, it requires that the consumer of the art invest some effort in understanding it. The payoff to the consumer is they gain a new insight or feel the artist's conveyed emotion.
Pop music is not considered "better" art because it is often formulaic and designed to sell albums. Being derivative it often does not break new ground artistically. It's easy to consume (listen to) because we know what to expect musically. It's sorta' like comfort food. Listening to music that is ground breaking can often be difficult the first few listens, but then you get an "ah ha! Yes!" moment, and as your ears and brain realize what's going on, it becomes enjoyable. Then, other musicians copy it, make derivative versions that push the concept a little bit further, and you have a new genre.
There ya' go. My layman's answer. ;)