Just a quick thought on why we’re alone or at least we think we’re alone! If you have read the Three-Body Problem sci-fi trilogy, then you may compel to agree with the author that other aliens don’t want to be seen at all costs! The idea is that once an intelligent world is discovered it could be the end of it.
Imagine an intelligent world that is being developed to the point that it needs to colonize other planets to sustain its population and civilization. This world thus would go out of its way to strip resources of other planets and stars. The hungriness of such a world would not be stopped and it would grow infinitely until their technology got so great that they could outstrip an entire galaxy for resources.
Aliens might not want to see such a world develop to such a capacity that would compete against their own world, so destroying an undeveloped world as fast as possible would be the easiest thing to do. Of course, we could not know what the aliens would think. Perhaps some aliens out there prefer peace over war. Perhaps, some aliens prefer to see the whole universe teems with colorful civilizations.
Personally, I think there could be aliens out there that are so developed and advanced to the point that they could hide in plain sight and we just don’t have the technology to see them. Some aliens could be so advanced that they don’t need to colonize and change the ecosystem of a planet for survival because they could modify themselves to fit into any environment! For all, we could know they could fly in a poisonous gaseous environment and would still feel like taking a stroll on a warm Sunday afternoon.
As we’re looking for a Goldilocks solar system to test our theory of finding existing alien life, these aliens may just be in plain sight but we won’t know it as we’re too focused on the wrong environment. In short, we’re guessing but we could be off for miles. Perhaps, aliens don’t live in a Goldilocks environment? Perhaps they are and they have the technology to prevent us from seeing them or seeing their solar system.