There's an aggregate side access road in the upper right of the photo next to the white coated concrete sidewall. This is the way out. The lower right section in the photo does not have an access road but a steep embankment (you can see the dried tree branches in the photo), so this would not be the way out.
When they fill in the leveling concrete on both sides of the "stay forms" of the drain section, the crane will have a flat surface to drive across. Cribbing will be laid ahead across the drain channel(s) and the flat concrete to protect the leveling concrete from the tracks as is currently set upon.
You can see that the crane is already straddling a drain section (left side image - tracks).
Notice they have drilled and placed the anchor bolts to left of the crane. They haven't placed anchor bolts to the exit path of the crane (to the right). This reveals the "exit" direction.
With one crane centered in the spillway, they save having to use two cranes on the sides. You can see one of the side cranes in the left of the photo. This side crane wouldn't have the heavy lift, and possibly reach, to work the other side of the spillway.
Logistics.
But I like the "Dean's office" answer the best.
Good planning and logistics. Many underestimate what a non-trivial task it is just setting up and relocating equipment of the size being used on the site.