I think the problem is that most aliens know that they have plenty of time to colonize the galaxy.

Take us for instance. It's taken about 9 billion years for our planet to form and for us to evolve almost to the point where we can start sending out colonists. And it'll take us only one or two million years to do it. So after 9 billion, if we wait around one million more were not gonna miss our chance. We could get alot of good reading done in that time and we could basically troll the entire internet. Then we'd more ready to get some real colonizing done.

In general species only change when they have to. Like when there's a war or when something paved over their wetland. So were gonna have to wait until we have to, like when the sun gets too big or when Andromeda hits. It'll be really great if we're spread out when Andromeda hits, in about 4B years. Lotsa stars'll get flung all over the place and which'll give us free rides to other galaxies. So if we just hang around at the beach for 3B years, then spend the last billion colonizing we'll have about 1000 times the span we need.