Some people still prefer and only use MIDI DIN.
For me, it's only partially about that. I dislike USB midi because it's generally less reliable, but the bigger issue is that I have a Polyend SEQ and the way it's interfacing with my MacBook Pro and MOTU midi interface it only behaves perfectly with physical midi DIN input meaning I need to use keyboards with physical DIN out. And I'm certainly not buying a series of USB-C to regular USB to MIDI adapters.
Anyway, I was all set to buy three or four Seaboard Blocks to put together when I found out no MIDI DIN. I know I'm far from the only one that prefers MIDI DIN out from any controllers (one of the primary reasons I bought an Arturia Keystep).
I hope Roli consider implementing this if they ever make a revision to the models. For now, I'll have to buy elsewhere.
I agree that a midi out would be helpful when you have a large studio with lots of midi devices. Perhaps a new utility block could be created which is a midi port? Not sure how easy this is though because of the MPE nature of the blocks?