I mean, they have to convert the digital signal to optical and back, all with electronics powered by the amount of current provided by the HDMI standard. How long of a run do you need? I've had luck with regular copper runs up to about 35 feet.
Okay yes some of it is. But in this case I need to run 4K video 25 feet to a projector, only way to do it reliably and relatively future proofed is fiber.