Honestly I do not understand that you really would not understand. So here is a typical example of why developpers do build on top of proprietary platforms: startup creating hardware which gets interest almost exclusively from the industry where due to all kind of reasons a common proprietary platform, Windows, is used. Hardware came first and then at one point early on they have to decide what toolset/frameworks will be used for lowlevel and toplevel applications. But really there is not a lot of choice at all: either do what the others do and develop for Windows and as such assure customers will come in, interoperability with other hardware is easy and so on. Or do 'the right thing' and go open source which has the benefit of open source but that is about it. Good luck finding customers willing to embrace your product and use it in their production lines if it runs on some, to them, alien platform of which they couldn't care less what license it has and if there is no straightforward way to make it work together with the hardware they currently own. So basically you are choosing between keeping your startup alive and well and making an income, or bakruptcy.
