Nice collection! I also really liked your own answer at the end.

I know 30 is a nice round number but if you are interested in adding to your collection I have a family of solutions you might be interested in. I call it the “Alien Adopt-a-World Program"!

We generally assume that if there are aliens then they’d have every reason to make contact with us or reveal their presence. This isn’t a good assumption IMHO. If we assume aliens are intelligent then it makes sense that they’d have minimum requirements before engaging with a more primitive species.

For example, maybe we need a minimum level of organization like a space port or a world government to handle visitors. In space there are no outlines of states and countries so where would they land? I doubt they’d risk it with a large portion of the planet being impoverished or in civil conflict. They probably know that coming here may cause further instability and perhaps a self impossed apocalypse.

Probably the most troubling is a minimum requirement for intelligence. Technically we still don’t know or understand what intelligence is yet. If we cant find intelligent life here on earth in each other, then there is no garuntee we’d know what we are even looking for in the cosmos. It’s possible then that aliens may not even recognize us as intelligent life.