The common ginger ale brands contain no ginger.

Are you sure about that? What do you consider the common brands? The one that most immediately comes to mind for me is Canada Dry, which does contain ginger extract.

Out of curiosity I checked, and Canada Dry is about 2% ginger extract. I’m not sure what the ideal percentage of ginger should be, but that seems kind of low. Given that they’ve been sued over this before, I suspect that this might be just enough extract to cover their behinds.

My go to brand, Seagram’s, contains “natural flavors”. Content and concentration unspecified.

The ginger extract is in the "less than 2% of" category. I found this:

"They do buy actual ginger, but then what they do is they boil it in ethanol, and that essentially destroys any nutritional or medicinal benefits," Mark Canofari said, adding that Canada Dry uses a ginger concentrate. "One drop fills 70 cans [...] and a drop is .05 ml. So that's how little, even of the concentrate, is actually in one drink."

https://www.foodandwine.com/news/ginger-ale-canada-dry-medic...

thats why i brew my own lacto fermented ginger beer/ale from scratch. the flavor is way better than anything in the store. I particularly like brewing ginger ale/ginger beers with molasses. it taste like gingersnaps.