I think the air is full of H and O atoms, but why don’t they combine to form water?

Answer

Hello Hans-Otto

I guess I have to disappoint you, H and O atoms are not in air.
By the way, these atoms are not stable, they quickly react with each other to form something else, as you yourself suggested.
The main component of air is nitrogen (N2), almost 80%, oxygen (O2), slightly more than 20%, and all the other substances less than 1%.

The exact composition (although it is not completely constant) can be found on the websites that you will find on the right.