I think a lot of it has to do with how MS has dealt with add-on developers in the past. After FSX was abandoned by MS, if you wanted new functionality in the sim you had to build it yourself. So add-on developers would all have their own propriety tech for things like Avionics, nav and the flight-model.

Today MSFS is constantly updated with new functionality, so you can just focus on your project, but old attitudes remain.