Wheelchair ramps aren’t limited to wheelchairs. I have above average hearing despite my advancing age and I choose to apply subtitles to digital movies about half the time because it provides me a better more enriching experience. Solving for color contrast limitations benefits everyone even when people have perfect vision.
There are no blind soldiers in the army yet all Army digital communications are required to conform to federal regulations that accounts for accessibility. The result is higher quality products with greater availability.
Usually the best argument opposing accessibility is that the authors/developers don’t know what they are doing. When they say accessibility is too expensive that’s what they really mean, and it’s not a good argument.