How come it is always "Designers Will Code" and never "Developers Will Design"? Is there some sort of assumption that it is easier to teach a designer to write

How come it is always "Designers Will Code" and never "Developers Will Design"? Is there some sort of assumption that it is easier to teach a designer to write code than have a developer learn to design? In my experience the best designers are not the ones who write code but understand how their designs actually transition to the implementation. They structure their mockups and comps so that all the pieces are divided up in their mind in the exact same way a developer would. At that point it becomes the inevitable monkey work of cutting assets and implementing them but because the designer and developer are on the same page there is very little friction. The designer doesn't know about the code written and the developer doesn't understand how the designer chose those colours, text sizes, gradients, spacing, etc but there is a simple common language that allows them to bridge what they don't understand.