Did see and hear the ukrainian An-70 UDF-Transporter flying at the Berlin Air Show ILA. Wasn't too noisy. (4 engs!) Noise can't be the reason for abandoning UDF designs. Low fuel prices like somebody mentioned above is what I think is correct -aside from the unwanted "propeller-appeal" many airlines try to avoid.
That An-70 looked like a good concept to me. However for other reasons they are getting late on starting producing it.