Yes, this is the key distinction: old software that works vs old software that sucks.

The one that sucks was a so-so compromise back in the day, and became a worse and worse compromise as better solutions became possible. It's holding the users back, and is a source of regular headaches. Users are happy to replace it, even at the cost of a disruption. Replacing it costs you but not replacing it also costs you.

The one that works just works now, but used to, too. Its users are fine with it, feel no headache, and loathe the idea to replace it. Replacing it is usually costly mistake.