Actually, for audio 75 ohms is not a requirement.
75 ohm is a standard or video/rf and perhaps "digital" cables, although the need for that last one is beyond me. I've used 30+ year old nasty, thin, stiff and yellowed audio cables for a digital coax feed with no problems.
In the past, before ditital and video came into play, audio cables could range from anywhere between 50 and 110 ohms and there were no complaints of problems.
Since the advent of these newer technologies and their requirement for 75 ohm cables, it's more economical for the manufacturer to simply use 75 ohm for everything. All they need do now is just change the color of the RCA plugs on the ends and slap 'em in different packages. ..with different prices too, I assume.