They are very concerned about secrecy. It's just part of the culture; you know it when you sign on. Apple is quite supportive of Open Source in an official cap

They are very concerned about secrecy. It's just part of the culture; you know it when you sign on. Apple is quite supportive of Open Source in an official capacity. I would actually say that the best talent almost certainly does not work on Open Source projects in their spare time (though quite a few talented people do get paid to work on Open Source projects). The "best talent" tends to have other hobbies outside of coding -- well-rounded individuals make better team members, especially when working with non-technical team members. A lot of young engineers don't appreciate this until they're older.