I didn't say easier.
Piling is up coal is of course very easy, building grid scale electricity storage is not, which is why we did one centuries before the other.
Moving all that coal about and then moving it again to where you need it etc. adds in loads of loss. So just storing your big pile is inefficient, even if a pile doesn't actually lose any energy by being a pile. Petrol is worse in practice because the storage is more complicated than a pile and there's a lot more distribution involved. It's not very efficient to store.
Batteries on the other hand lose energy just sat there, but you more than make up the loss in practice by not having to shift electricity by the tonne.