A simple question really.

If anyone knows the reason, I would be interested to learn the answer.

Now that their is a Fallout game without them I really am missing the varied looks like:

Merc Cruiser and Adventurer which where two of my favs.

Gunner stuff looks pretty mercenary-like

The Gunner's attire is very military inspired, despite the fact they are a Mercenary group,

Irony much.

The Gunners are the best mercs BECAUSE they're like the military. Ever heard of Blackwater (though they don't call themselves that anymore)?