men, you dunno what your talking about...
Because they make the tools you use right now. The tools you love and hate. Or perhaps the tools you have envisioned in your mind. Dreamt about.
If you pay a developer to collaborate with you, will be amazed at how far your ideas can be pushed.
Because you're not a developer. Developers need graphic designers, as graphic designers need copywriters, as copywriters need illustrators, as illustrators need a pen.