Aesthetics? Because it's expected?
I had no "expectations" as I had no idea what Bob would build. He asked what use I had for the pistol, and I told him metallic silhouette, and some action pistol. The guide rod choice was his - not mine, and I didn't expect to find a full length guide rod.
While that sounds, on the surface, logical - I have a hard time believing that was the reason - as a full length guide rod would add about 0.0083% to the overall cost. Not exactly what you'd classify as a high profit add on. But, I suppose every penny of profit does count, so I guess you could not rule it out.
Aethetics? Okay, that certainly is a possibility as the pistol does look different from the front because you have a recoil spring plug with a hole in it for the guide rod - that certainly does give it a different look. Bob used a flat-wire recoil spring, but I would not think that would make any difference in the choice of guide rod.
In any event, to me, an interesting choice given the that there is is little profit and no apparent performance improvement. Next time I talk with him, I'll ask his reason for using it.