Music is art.
Art is about expression, about sending a message to the listener or viewer, a message with meaning that can be interpreted and reflected upon. This doesn't have to be a discrete message, I'm sure I get something different out of Lucy in the Sky with Diamonds than you do.
Music remains art as long as the artist has creative control over their work. They are free to direct their message as they wish, and if they are clear enough about what they mean, and have the skill to execute it, can pull off something of amazing quality.
However, with most pop music (and some music of many other styles), the aim is not to create meaning, but to sell records. Therefore, the musical process is inherently corrupted from the very beginning, and the resulting piece of work becomes of minimal artistic value.
There is nothing wrong with writing and playing accessible songs, but if the aim of what you are doing is to make cash, you are in the business for all the wrong reasons. This is why Jon Bon Jovi sucks dick.