Every workhour that is put into the MP is a workhour that the SP will be missing. Just look at ME3 and its pathetic N7 missions.
A lot of the logic so many of you people use is really flawed. You do realize that when an artist designs specific assets for SP it can be recycled for MP as well. The animation team that mo-caps moves can also be transferred. The post processing done for various effects such as fog, rain, among others can be used both ways as well.
They have a vision with the essence of this game and if any team is capable of making that vision come to life it's SSM.