"Traditional" isn't really defined here, but seems to mean "first half of the 20th century," which feels like a relatively narrow tradition. Not a lot of preference for teepees and yurts.
But this is a reasonable point to raise. Although both would serve their purpose a concrete viaduct is much cheaper to build than a masonry one, to the point that it may be difficult to justify the latter no matter how strong the public preference is for it.