The 15 threshold end of the runway is ungrooved concrete which has the potential to be slippery when wet.
That was my intial thoughts as soon as I saw the thread having had a couple "oh heck" moments on it as well.
It isn't the first or the last plane to slide on it. Its not part of the live runway could they not put some shell grip or something similar on it preferably in a none grey colour.
On another note its a bit of a sod to see planes which are lined up on it as well if they have a light colour scheme.