For simple grid storage the efficiency is just bad. The electricity-hydrogen-electricity round-trip efficiency is about 60%, pumped hydro or batteries can do better.

So it's only worth it if you have other uses for the hydrogen or need longer-term storage, e.g. gas reservoirs.

Plus any infrastructure you build will have to be overprovisioned because by definition it'll be designed to absorb peaks and run idle the rest of the time, which makes it even less profitable.