Because hamburgers are food, food is a natural requirement for people to live and is a limited resource. Not to mention the amount of processing that is REQUIRED by most governments to adhere to standards for meat preparation, delivery, and cooking. You're discussing a limited resource with much much more overhead and regulation.
This is a service, arguably in our society one that people find necessary for job standards and such. There are recurring costs such as equipment, building rent, utilities for the building, and again....health and sanitation standards to adhere to.
Again, another service with a sense of urgency or necessity. People NEED plumbing to work in order to have proper sanitation in their homes/businesses. It is not a frivolity.
The radio in my car was free
What it boils down to is that music is NOT a tradeable commodity or a necessary service, it's a work of art and the value is not dictated by supply/demand, but what the individual is willing to pay based on perceived value. Music can be delivered in many different ways, but as you read up there with Cracker...we're not talking about a whole ton of money when you consider costs incurred, taxes, and splitting it between all the band members. To cite specifically, the guys from Scale the Summit (according to their frontman, Chris Letchford) make most of their money on merch sales...and according to them this is what most of the smart bands do when they want to turn a decent profit. They are on a major label (Prosthetic Records) and are in the upper artist tier. You gotta cover all the bases you can because pennies make dollars, but the ability to let people hear your music for free will make exposure much easier which may lead to concert and merch sales. It's your art, market it how you want, but I've always resented that "You're stealing from the artists!" attitude that major labels try to push out...you're not greasing their exec and marketing tool's pockets, they are who are robbing the artists blind, not people downloading their music for free. Just my $0.02