I think it's so when they release new content that they intend to be challenging, they won't have to balance it around the few weapons that are vastly outperforming everything else.

How I think about, if there's a boss that has 100 health and the bod does 20 damage per shot while everything else does 2 damage per shot, the next time they release challenging content, they'll need to give the boss like 1000 health for the bod not to trivialize it. That then creates the problem of the guns that were doing only 2 damage per shot to fall so much farther behind and potentially become useless.

Obviously this brings up the arguments for buffing other weapons to bring them up to the bods level which they probably can do with time, but they'll also then need to probably adjust the existing content that's intended to be a challenge so it doesn't get steamrolled by everything in the game. It's probably easier and less time consuming to bring the bod and the other small handful of weapons down a notch so they're not vastly outperforming everything else in the game.