We humans are creatures of flesh and blood - or of carbon molecules and liquid water, to put my nerd hat on. We live on the surface of a planet, and we get heat and light from our local star, the Sun.
So, when we look into space, it's natural that we look for carbon molecules and water, at the surface of other planets, warmed by their local stars. It's just logical - we're looking for what we know we'd recognise.
But it means we're missing this:
That is the structure of the cosmic dust in our galaxy, as seen by the Planck space telescope. the different colours correspond to different temperatures in the dust - and as you can see this ultra thin soup, made of electrically charged gas and cosmic dust, is what fills most of the apparently empty space around us.
And if it seems like dust and gas can't be that important, consider this picture:
This is a star, and probably a whole solar system of planets and moons, condensing out of the interstellar dust and gas clouds. Just like the Sun, the Earth, and us.
Just to make sure you realise how important tenuous gas and electrically charged dust can be, a few years ago a computer simulation showed that such clouds of dust and gas could produce life.....