As the picture below shows, the Welcome Aboard mission is available for all members of the public Oracle community, as well as members of MOSC. Everyone has access to the public community, obviously, but not everyone has access to MOSC.
Since all points are accounted for in the same global leaderboard, it creates a disadvantage for people participating in the public community. The same applies to pursuing different strategies. Participants of the MSOC community, for example, get points for responding, unlike in the public Oracle community.