Those products don't need to be complex, at their heart they are actually rather simple. They are just written in such a way that they become unnecessarily comp

Those products don't need to be complex, at their heart they are actually rather simple. They are just written in such a way that they become unnecessarily complex, because they are poorly understood. I would argue that the examples you give don't work well (Windows, Android, Chrome, later versions of iOS). They get worse and worse over time. Even if they start out with a good design, it turns to crap eventually. Just because a piece of software is used by billions doesn't mean that it is well written.