Under hood paint

That is a good question. It is not for me, but then again, some people have other ideas.
1. Maybe they think it looks nice. They like it.
2. Maybe the engine bay has some serious problems and that was the easiest patch available.
3. Maybe they don't think the orange or turquoise engine clashes with the body color.
4. Maybe they are on a tight budget, and they had to cut a corner.