There are some (very few) cases where it makes business sense. For example, the company I work for has software developed in a legacy language with no support

There are some (very few) cases where it makes business sense. For example, the company I work for has software developed in a legacy language with no support (Forte 4GL). There are companies that offer Forte to Java migration, it would have been worth it because of better tools and support (even if the code was the same crap as usual :) ).