[mrep]

And this is where the supply side of the equation comes into play. Many people can build the road and there shouldn't be any differentiation in how it is built (assuming they have common engineering standards). Thus, the supply is almost perfectly competitive causing low wages.

However, there are infinite ways a developer can make something. 1 developer can make design a system that can save/make their company millions that most other developers would miss. The supply side of developers is more like a monopolistically competitive market. Thus, they can extract some of those savings/profits in wages.