We can't predict motivations of other forms of life, can we? They are completely different (in theory). They even can build a trap to make evevryone who will get there happy. Or to hear their story. I dont know.
They are products of evolution and, in theory, we'll be very alike in many ways.
But then, maybe a species able to colonize a galaxy can only appear as consequence of those rare exceptions. We, as a not completely selfish species are evidence for that.