The problem with the fine grained user control over individual theme colors is that the OS theme is never complete enough for applications with visually complex

The problem with the fine grained user control over individual theme colors is that the OS theme is never complete enough for applications with visually complex UIs. At some point, applications have a need for extra colors to denote things in different ways. So they would need to provide their own configuration UI that allows the user to update these colors to be usable with any custom theme they're running. Unfortunately, most software developers never bothered to implement something like this and assumed the user would be running the default theme. So the users ended up with lots of broken UIs after trying to adjust the system wide theme.