The difference is the ‘L’ in LPG. It turns liquid at a relatively low pressure and takes up much less space then. Hydrogen does not do that, so it has to be stored at a much, much higher pressure. For example, a medical oxygen bottle or a scuba tank has around 200 atm of pressure. For cars, hydrogen is usually stored at 700 atm. And the pressure inside an LPG tank is around 8 atm at room temperature.