Not all of them do: see https://en.wikipedia.org/wiki/Diamond_open_access which charge neither readers nor authors. In TCS, see, e.g., https://en.wikipedia.org/wiki/Logical_Methods_in_Computer_Sc...
But somebody's doing the typesetting. Giving sufficiently technically competent authors that could be the authors, but otherwise some money has to be found from somewhere. I don't mind that coming from libraries or research grants if necessary: it's cheaper than Elsevier.