We surely know how strong rubbermarks looks like but, as usual, this was made for performance reasons.
They way they are now, the cost 0% in performances, since they are embedded in the runway texture itself, so no extra polygons are added. If we made them as in real like, they would require
- extra textures that would cover a big (if not all) part of the runway, to represent their changing shape along the path
- extra polygons to map the extra textures
Semi transparent ground polygons drawn on top of other Semi transparent ground polygons can be quite expensive to draw, especially with anti aliasing, that's why we opted for a more subdued effect, which costs 0% in fps.