Legacy code isn't necessarily bad - it may just be complex, or poorly documented, having accumulated a lot of production fixes over the years that were never properly documented (if if the original project was - typically not).

Your legacy code products may be happily running without problems, due to all those production issues (incl. new requirements) that were identified and fixed over the years, with the problem only coming when there is a need to change it, especially when there is no-one left familiar with the codebase, maybe not even with the language/tools used to build it.