Why would someone drop CSS as their skill when they know other frontend bits? Designers don't need to know HTML/CSS when frontends can just build it up from im

Why would someone drop CSS as their skill when they know other frontend bits? Designers don't need to know HTML/CSS when frontends can just build it up from images. It's a weird place to draw a line that designers need to pass the result as HTML/CSS instead of just the image file.