Obs30 I can understand why ZWO is reluctant to share openly their software developments.
They may well be reluctant, but that does not absolve them of needing to publish changes that they have made to the licensed open-sourced software.
Open-source does not mean free. It simply means that the source code can be openly read and used. Many open source license (the MIT license and the Apache license are exceptions) come with a requirement that any changes that you made to the source needs to be pulished openly somewhere (github, for example).
Even libusb (used by almost anyone supporting a USB device) is under LGPL license. But if ZWO is just using it as a library, without altering the sources and recompiling it to better match their camera needs, then there would be no sources to republish.
By the way, in addition to StellarMate, you can try INDIGO Sky too. For those who use Xcode and macOS to develop code, INDIGO Sky is arguably a better path than StellarMate.
Chen