I code for thousands of mostly-unique commercial software products a year, using 8 languages (mostly C#), for many dozens of major customers, and lots of smaller ones.
Because of this, I have a huge chain of demands I keep track of, and methods of automation in order to collectively manage a constant flow of data requirements, and of course tracking issues both shared and common between these scenarios.
When I'm coding, I've got to code in a way that communicates these details to myself, consistent between all the languages I might have to touch for coding, scripting, database, reporting, and specialized languages a client may suddenly require.
Because of that, my code has to be a loose framework, a late-binding train station of logic, where demands may switch at any moment, and limitations imposed from other teams may similarly pop up.
My code is littered with multi-paragraph discussions of a technology I once had to interact with (customers often switch back), large sections of functions commented out rather than deleted, and other 'bad' practices just to give me landmarks and a 'flavor' of what a customer is occasionally interested in, amidst a never-ending avalanche of context switching between products and customers.
I've redesigned these several systems from the ground floor once (they used to only handle a small fraction of the work, using an antiquated language), and am working with a team to do a better design... but it's been very difficult for a team of perfectionists to understand how to react to an unlimited flow of changing requirements. Fortunately, the code itself has been quite usable, and they're using the same languages, but no system can really handle these demands truly consistently - I'd call it NP ridiculous. It's basically the "mythical man month" writ live, where I've got to do my work, and train a team whose work process may never really be able to do what I can do - definitely healthier long term, but can't help but result in some amazing process failures.
I actually would have made most of these design changes myself, but at the time, I was forbidden by management from making those choices, since I was doing my work directly at the production level - so it's actually a bit of a relief to see someone at least allowed to make some of the better choices.
In short (and yes, for this scenario, this is short), because I'm doing alone, for years, what a team of almost any size would struggle to approximate, as many of us seem to be doing, I've got no choice but to code how I need to in order to have a system that I can sanely maintain in an insane set of requirements. There's not really a choice in the matter, if your put in a position where "oh, we suddenly need this" exists as a live production task in a growing industry.