Players get type cast as defensemen very early in their hockey careers, and stereotyping, stubbornness, and hockey tradition largely prevents position changes.
But forwards are just better at hockey, generally. Faster, better with the puck, better at scoring and creating offense and driving shot chances - these are the reasons that they get put up front in the first place, way back when they are wee little lads.
Progressive teams could benefit by drafting less unskilled defensemen and converting some skilled forwards to the blue line.