They have already made the styles for their keyboards and paid for them by selling as many keyboards as they could.
No extra expenditure except to make the module
They (and you) will never know if the demand is there unless they try.
Korg owners think they are good so I would buy the module.
I don't have room for any more full keyboards but have 4 modules and would be happy to add to these.
The same argument applies to Yamaha too.