Why isn't hydrogen commonly used as fuel?

There are two main difficulties in using hydrogen as a fuel. First, it doesn't occur naturally on Earth anywhere, so it must be produced through either electrolysis, which takes a lot of energy to do, or from extraction from methane, which produces greenhouse gases. The second difficulty is storage. Hydrogen is a gas under normal circumstances. However, for fuel purposes, it must be stored as liquid, because as a gas it takes up too much space to be useful. To store it as a liquid, it must be either under very high pressure or very low temperatures, which as it turns out are both difficult to achieve with hydrogen.