Coding agents write flawless markup and then guess at the pixels. There's no surface for them to look at what they made, judge it, and fix it — so design still snaps back to a human, every time.
Agents emit UI as text. They can't render it, so they can't tell good layout from broken.
Every task starts from zero — colors, type, and components re-guessed instead of reused.
The jump from "looks right" to shippable code is manual, lossy, and slow.