Nobody sets out to make an unmaintainable mess.
Probably the most common complaint from software engineers is that they never have the time to eliminate technical debt. Productivity and velocity go down, bug rates go up, product performance plummets, and customer complaints skyrocket. Technical debt is always related to complexity, and hidden complexity is still complexity.
Years ago, my wife overheard a conversation at her hair salon, between another client and a her stylist. It was funny because they were both talking about the cost of a purchase, but they didn’t understand each other. One of them thought that the cost was the same as the price. The other thought it didn’t cost anything if their minimum monthly credit card payment didn’t go up.