While you're not wrong that a crystal radio does work without power, you do actually need to have a crystal radio in order to use one.

There are probably more homes with a charged USB power bank that could power an FM or DAB radio than homes with a crystal radio or the means to build one.

Yes, it is not generally available but as an anecdote I mentioned crystal radios because I don't know that from my technical school or university degrees but thanks to my grandfather who didn't go to an university.

I’d personally use one of the ham radios charging on my bookshelf. If I were to ask my wife to pause while I whipped up a crystal radio, I’d likely be the first casualty of the disaster.