Why does the "runway start" arrow float above the runway?

There are a lot of things that confuse me in the scenery editor. One of those things is why the green runway start arrow hovers above the runway by default. Floating above the runway makes lining it up against a centerline or a taxiway point very difficult.

Yes, I can grab that green arrow in the gizmo and bring it down to the ground. But what benefit is there to having the arrow sit above the runway to begin with?

There are many items that either float above or below the ground that correspond to items on the ground, and I’m confused about all of them. I’ll start with this one.