True, but email is pretty crufty with headers and markup, and that compounds with the flotsam of unread spam retained out of laziness, and for the sake of completion. Not to mention that duplication occurs with the endlessly indented prior messages retained in lengthy reply chains across all conversation participants. Compression of that kind of information helps, but compression only attacks the problem only in the usual blind, robotic manner.

I’d estimate that high definition video has similar problems, in that 24 hours of a pitch black screen with an ambient noise floor, captured at 4K screen resolution, and 240 frame rate, would still eat up 1TB, even with an efficient codec, because imperceptible thermal noise in the frames leaves a lot of uncompressible variation in the pixel raster, even though the actual color differences are imperceptible to people.