Has nothing to do with operational considerations, but instead, economic ones.

It takes a lot of passengers to fill a 747 day in and day out on any one route. Obviously the airlines serving DFW don't think the economics work, or they would be flying them.

American did fly 747's to DFW from LAX in the early 1970's for a short period. The biggest 747 operator at DFW was the original Braniff, also back in the '70's. You could catch "Big Orange" to Honolulu daily, and later on they flew them to London, Paris and Frankfurt as well. I believe Delta also flew them for a short while between DFW and LAX/ATL.