That is what I am thinking
I can’t tell if there are any gullies in the crater wall.
I expected to see such ice at the bottom of the craters that do have gullies, and I have been surprised we have not. The only thing I can figure that not enough water is released to pond. It evaporates too quickly. But somewhere, the might be a crater were there is enough water seeping out to pond and then freeze. Maybe this is one.