Why are pot holes left for so long?

I pass this 'pot hole' several times a week and for over six weeks my mind conjours up a good reasons why the road cones are still out and the hole is still there.
 It is kind of them to cover the whole with this large steel sheet. Stops cyclists falling in. Asking around I can't find any reason why it is still open or why it was opened up in the first place.
Further along the road I found the culprit parked up on Sunday protected by rough ground only approachable by MTB.

Why are they left open for so long?