Ohh... But look at all those assumptions you've gone and made!

1. Extraterrestrials are not now living among us.

2. The population density of Intelligent life is high enough that it is practical to commute.

3. Aliens can survive away from the planet's surface. (Low G isn't healthy for everyone).

4. Aliens are not xenophobic pacifists.

5. They find us interestering (But they're intelligent! Exactly...)

6. They reproduce fast enough to populate the stars.

7. They can see us. (Meat?!)

8. There is a spoon.

9. They would come at the right time and/or stay long enough to intersect with human civilization.

10. The life cycle of an intelligent species is long enough to leave a star system. (We're almost there... Cut it out with those nukes!)