> What you list are common characteristics encountered in legacy systems, but what makes it legacy is a business decision of declaring it obsolete and in maintenance mode, and so that no money or time to be invested in it.

No, not necessarily. Business decisions are one of the many factors in creating legacy code,but they are by no means the single cause. A bigger factor is developers mismanaging a project to the point they became a unmaintainable mess. I personally went through a couple of projects which were legacy code the minute they hit production. One of them was even a proof of concept that a principal engineer, one of those infamous 10x types, decided to push as-is to production and leave two teams of engineers to sort out the mess left in his wake.

I recommend reading "Working Effectively with Legacy Code" by Michael Feathers. It will certainly be eye-opening to some, as it dispels the myth that legacy code is a function of age.