That's because there is not much stuff in the universe, and whatever there is, tends to cluster together under gravity. But within such a cluster, if you create empty space, something will want to rush to fill it in.

Physically too. But it's a question of perspective: glass half-empty or half-full. Are planetary systems plentiful? It seems so, as a ratio of all star systems - as far as we know at least. Definitely not, as a ratio of the total volume of space. Similarly, the idea that we are mostly vacuum, because the elementary particles are so small compared to the size of molecules, etc. But that doesn't much change our intuitions about solidity vs. emptiness in every day life.

The way I see it, space is a life-vacuum, and human nature is to abhor that, as evidenced by the long-standing goal we have of interplanetary/intergalactic settlements.

Which is to say: you’re thinking on the wrong timescale. Just wait and see. :)

No one ever said the vacuum has to be filled biologically. The universe is a vacuum but even there you get spontaneous virtual particles getting created out of nothing as far as we know.