Why do dairy cows like to hang out on large piles of manure?

They dont, animals dont like to be dirty, especially with dairy cattle it is important that the udders stay clean and healthy. Now I have seen cattle that preffer the hard floor as apposed to the soft bedding that could be because of heat (they find the floor cooler), but she is not laying in large piles of manure.

If diary or any animal are laying in large piles of manure than there is a risk of the operation getting shut down.