WHy the fuck did you changed that? I mean serious.
The developers currently have no way to make stats on parts different depending on if there's a certain combination of parts.
The Jailbreak together with a barrel sticking out infront of it will mean that the Jailbreak is nothing but an extra weight, it would essentially do nothing.
So instead of putting the problem on the shelf and wait for a system where certain parts change stats depending if another part is equipped at the same time, they just restrict you from putting that stupid combination of items together in the first place.
100% correct explanation here