Immediately after salting the salt rests on the surface of the meat, undissolved. All the steak's juices are still inside the muscle fibers. Searing at this stage results in a clean, hard sear.
Within 3 or 4 minutes the salt, through the process of osmosis, will begin to draw out liquid from the beef. This liquid beads up on the surface of the meat. Try to sear at this point and you waste valuable heat energy simply evaporating this large amount of pooled liquid. Your pan temperature drops, your sear is not as hard, and crust development and flavor-building Maillard browning reactions are inhibited.