You're missing a few key possibilities. Travel I'm space, why? Explore, conquer or survival due to lack of resources on home planet. Also if we did discover life on a other planet who knows what it will be. I'm sure there are planets with living microbes and bacteria, hell they survive near volcanoes here on earth. Possibly more advanced civilizations. If they're exploring I would imagine there's a possible unity among beings on their planet , some sort of peace to collectively use ideas and resources for the betterment of their species, existence.