The fights not in DF at launch require too much communication for your average DF group (especially on Japanese servers with their mix of JP and EN). 'I can at least try' - but it'd end up being detrimental to the game. The groups would be full of nothing but toxic players screaming at each other, putting each other down, pointing fingers etc and anyone entering this to 'see' the content would probably end up logging out. They're just nowhere near balance around being added to the DF until 1-2 patches later.