Do we really have to examine the origin of every word we use rather than according its modern common usage and use in context?
Open source people from other regions provide the majority of code and have no say in political decisions. One might be tempted to say that they are slaves.
This is a default. If it offends your sensibilities so much, you can configure it to be something else.
Heck, I'd even go as far as suggesting that "main" is a more common word for non-native speakers of english than "master", making it more intuitive for non-US developers.