Because, generally speaking, those people make enough per-gig to support an agent making a living taking a small cut. Furthermore the amount of time required f

Because, generally speaking, those people make enough per-gig to support an agent making a living taking a small cut. Furthermore the amount of time required for the comedian/actor/musician to complete the work is pretty small. If you can start charging 6 figures for projects you can complete in a couple days, I'm sure an agent would be happy to work for you. If not...