other position in non-game situations: Acceleration, speed, running routes, catching the ball. In spring, there are very few moments that could resemble anything like a full-on game situation where RBs, LBs, OL/DL could be properly evaluated. WRs just do a lot of 1 v 1 work vs the DBs and you can pretty much tell who stands out because their abilities can easily be put on display, even in the spring without full pads. That's just my guess. In the fall when there are more 11 v 11 game situations in full pads, we'll probably hear much more about linemen and RBs starting to stand out.