Your statements correctly point out that extraterrestrial life is possible. That does not mean it has ever been here. If it has been here, there is no evidence of it.

Our imaginations may dream up technology. Nevertheless, imagining it and actually implementing it are two entirely different things. Consider this: 186,000 miles per second. That is the cosmic speed limit. No matter can accelerate to that speed. At that speed, it takes 100,000 years to cross this galaxy. Suppose, even with those limitations, they set out. Did they have time to get here? Why would they come here anyway? They can explore the universe the way we have been doing it, by looking. Light is pretty cheap and the fastest known thing. It makes sense to develop that science rather than spending eternity driving around.