Vastly more efficient at storing electricity. Vastly more expensive to construct, using rare materials. Have a Vastly shorter lifespan than a hydrogen tank and much lower energy density. Everything is a compromise
Hydrogen has also terrible volumetric energy density. It’s also really heavy until you scale to huge tanks.
Europe has enough salt formations to potentially store millions of GWh of hydrogen, far more than would be needed.
Liquifying hydrogen also costs you another ~10-13 kWh /kg where Hydrogen only contains 33kWh if you want heat, but more like 10-15kWh/kg if you want to do useful work. So you’re roughly paying double the energy for the same amount of energy stored.