Steinberg did not do the drivers, they did not have the needed technical info from the OEM manufacturer or the driver source code, one of their employees literally hacked the unit to get a compatible 64bit driver, unusual but in my mind praiseworthy of them to release them at all
They could not release a driver source code they did not own, why is that so difficult to understand? You can only release source code that you own all the right to and this has been explained by Steinberg and others time and time again.
And BTW the Midex has nothing to do with Yamaha, it was released before Yamaha bought Steinberg.