Your work is amplified through the action of the corporation. This isn't just true of software developers but even repetitive manual labor on an assembly line is amplified through the co-operation of the group or corporation. Your compensation for this behavior is reduced risk, that is to say the corporation assumes the risk around your quality of work. So they basically pay you or someone else to fix problems you create.
A carpenter, brick-layer, whoever doing a one-off job is doing that job under the assumption that they bear the risk of quality work directly, and they do typically charge more for it. Maybe a good example is: if you've used a plumbing company with many plumber employees you'll find the plumbers are paid a wage rather than per job. That wage is typically less that the plumbers might be able to earn working on their own but the company offers some guarantees to it's employees, and the difference in wages is acceptable to the employee because they get reduced uncertainty of income and the work quality risk is assumed by the company - essentially shared among the other employees (somewhat) and shareholders (mostly).