#MiSTerFPGA isn't a product. You might buy products related to the MiSTer project from third party independent sellers, but MiSTer itself isn't a product like an Analogue device. It's still okay to compare the two but it's an important distinction to consider.
-
Depends on what the fork is trying to do. If someone forks the Genesis core to add 32x support nobody is going to be mad. Fork the NES core to add save states.. everyone will cheer you.
I concur the hostility is gatekept, and often seemingly tied to hardware partners at times.