Why should we have evidence when, as in your analogy above, we haven't looked everywhere and we don't have the tools to see everything.
Because we don't need to look everywhere and see everything.
God has never been, for example, a rock on the far side of a distant planet.
It's like I've said before, you don't need to check behind the fridge in order to know that your apartment isn't infested with galaxy clusters.
When we look at the cosmos, do we see any indication of God? No.
When we look at religious rituals, prayer, and such, do we see any evidence of divine or supernatural response? No.
When we examine the human body and mind, do we find any evidence that there's a soul? No.
When we examine scriptural claims about God, do they turn out to be accurate? No.
In fact, when we look at all claims about God ever made, do we find even one which holds up when tested against modern knowledge? No.
In fact, everywhere we look, and with every test that is possible to perform, we find that God is absent. The best that its defenders can do is to assert that God looks exactly like not-God, or retreat into their own individual mental experience, which isn't evidence for anything.
We do not need to test to see if God might actually be ensconced in a sand dune on a distant planet, because that's not the kind of thing that God has ever been.
We have tested the things that God was supposed to have been, and God has failed.
Why can we not simply admit this and move on?