I would think that the differential in costs when buying a recording (a song) or the cost of a live performance (concert) comes from the effect of hearing someone speak. An album is produced in a recording studio so the singer’s voice is processed and autotuned and mixed. A live concert is just that a live performance there is no machinery autotuning the singer’s voice you are hearing what they actually sound like, not what a major label wants the artist to sound like. I know of quite a few bands that are terrible live because their fans have gotten used to a certain sound that can only be created in a recoding studio. Therefore even though the costs of hearing a band live are much higher, it is one of the more intimate interactions fans can have with their favorite singers.

theoretically to record a live performance (concert or speech) would be considered theft, the talent is being paid by an institution to do what they do, either perform or speak, and by recording that for your own use and distribution you are stealing from what has already been paid for. The institution pays for the rights to sell tickets so you circumventing that you are stealing from them. However legally the only reproduction of the performance that would be legally defendable would be that which is recorded by the institution that paid for the original performance to happen in the first place, much like with book publishers buying the printing rights for works of literature.