Most likely the copies that they had have been broken or lost.
“Despite the size and diversity of our inventory, we occasionally find that demand for certain titles exceeds our best efforts to meet it. This is especially true of out-of-print titles and titles for which we experience heavier-than-usual breakage. As soon as inventory conditions permit, we will once again make these titles available. Customers who already have one of these titles in their Rental Queue and decide to remove it may find that inventory restrictions prevent the title from being added back into their Rental Queue.”
If you’re just looking to see it, you can watch it for free on here…
Mastroianni
Does anyone know? The Criterion DVD is still in print. I don’t understand why it would unavailable.