Why does macOS 10.15 Catalina still ship with Python 2?

Apple has announced they would deprecate scripting languages like Python, Perl or Ruby from the desktop edition of iOS. So there is no point in including the "new" version of Python (3). They're keeping Python 2 for compatibility with existing applications but they'll eventually remove that too (and potentially they will remove every single piece of technology that is vaguely standard or open).