Economics is only a part of it. Often, poorly built software increases costs for the company that built the software, like when customers call the helpline to get an agent to do what they could have done on the website. Or, when I call the helpline and the agent asks me to call again because their software isn't working today.
As another example, when I was logged in to my mutual fund web site, I found a button that says Get Statement. Since I wanted to download one, I clicked it, and it said, "Your statement will arrive in the post soon." They sent a paper statement without confirming me what I wanted. When it arrived, I threw it away, of course.
In many cases, poorly built software increases costs for the company as well, so financial incentives are only part of the story. Incompetence is another part, maybe a bigger one.
Considering the upfront cost has just as much to do with economics as considering the overall cost of high quality software. Economics is a description of human behaviour and all the irrationality and incompetence that comprises it so decisions of short-term gain vs long-term gain are very much included in the study of software from an economic point of view.
As another example, when I was logged in to my mutual fund web site, I found a button that says Get Statement. Since I wanted to download one, I clicked it, and it said, "Your statement will arrive in the post soon." They sent a paper statement without confirming me what I wanted. When it arrived, I threw it away, of course.
In many cases, poorly built software increases costs for the company as well, so financial incentives are only part of the story. Incompetence is another part, maybe a bigger one.