If you're a talented developer, but with no marketing or other such skills, you join a company. For the sake of argument, let's call it a Software Consultancy. Then the consultancy finds you Gigs (i.e. takes on projects and puts you on them), and you get money.
Companies, in fact, solve another problem that acting doesn't have - namely, actors are hired alone. Software, on the other hand, is much, much more likely to be built by a team. And having a team brings you all sorts of other difficulties that customers can't deal with:
* You need a team that works well together
* You need proper management of the team
* You need proper processes in place for building the software
* In some cases, even access to equipment is an issue
In short, an agent that can represent a single developer is not the right "level of abstraction" for most clients.