Presumably CVS works for them. They had used it successfully for 5 years before Subversion existed and are presumably well acquainted with its foibles. And all

Presumably CVS works for them. They had used it successfully for 5 years before Subversion existed and are presumably well acquainted with its foibles. And all systems have foibles, so if you are used to one set of them and it is working for you, then fixing things that aren't would seem to be a much better use of time, rather than following the whims of fashion to court those developers who will only help if they don't have to learn another versioning system.