I’m assuming because it’s a forced bet they didn’t want it to be a full small bet.Agreed. I just got home and was ready to cite some resources. I was also going to concede that perhaps it's a regional variant, but I think not counting as a raise is the more common version. As long as everyone knows and agrees on the rules beforehand, play away!
As an aside, I haven't been able to figure out the reason for the bring-in in the first place vs. just forcing the low card to put in a full bet, at least in a tournament setting. Most of my players are casual players with little experience who struggled with the bring-in vs full bet idea at the tables I wasn't playing at, so for my tournaments I got rid of the bring-in and just force a full bet and haven't noticed any ill effects.
One might say hold ‘em has a full-size bet as mandatory big blind, but that rotates and is equitable. Whereas if you’re unlucky in Stud you could be the bring-in many more times than if in a rotation, so by having the bring-in be smaller it doesn’t punish bad luck as much.
But this is just a total guess on my part.