[aseipp]

You need to use specific browser APIs (Service Workers) in order to support "offline mode" for a webpage, including support when there's no internet at all. This means the page and its content is stored locally for later, separately from normal HTTP caching.

Yes, if you loaded the page once into a tab and then never closed it ever again, then it doesn't matter so much and you could use it if your internet shat out, but in practice people close and then re-open things later under varying network conditions.