Are aliens watching us?

The Fermi Paradox allows for many explanations. One is that the human race encountered aliens in the past, we just don't know about it. This anti-anthropocentric view does not offer an answer to the question "are they still here?" If they came a long time ago then they probably went away bored. If they came recently they probably went away laughing. But perhaps they or their machines are still here, watching and waiting. Can we speculate for what are they waiting, and what would trigger a change in their posture?

They could be waiting for us to all kill each other so they can have the planet, or they could be waiting for us to dig up an artifact on the moon or Mars. They could be waiting for reinforcements, or for Sol to explode. They could be waiting for us to invent something they desperately need, or for us to answer an important question such as "What is the meaning of life?". Perhaps they are waiting for us to arrive at THE question for which they already know the answer (101010).

I believe the answer is much simpler, natural evolution produces one sentient species per galaxy once every 10 billion years. We are alone in the Milky Way and will be for a very long time. In fact we will probably colonize this galaxy so extensively that we prevent the evolution of the 2nd ones.

But it's fun to think aliens are listening to us and laughing at the method used in the USA for choosing leaders.