In the prologue in WOK it says,
"Szeth didn't own a set of Shardplate himself, and didn't care to. His Lashings interfered with the gemstones that powered Shardplate, and he had to choose from one or the other".
Is this because he gets his surgebinding from a "Honourblade"?
This what I think because neither Kalak or Jezrien are wearing any in the prelude, and the Radiants in Dalinar's visions are using their surgebinding while wearing plate.