Because it's been my experience so far that they, well, suck.
My friend tried to consign a SKS there a couple of months back (he had all the original stuff for it, never illegally modified or anything like that). They told him FLAT OUT that they will not deal with AKs or SKSs. "Because they can't prove that it's been illegally modified or not". Which is the stupidest thing I've ever heard, because that can apply to any weapon.
Fast forward to this month, I called them asking if they do gunsmithing services.
"Sure" they said, "what do you need done?"
I told them I wanted to get a Barrel extension permanently welded onto an end of a barrel.
"what weapon?", they ask. I say "An AMD 65 I'm building from a kit".
The guy says, "Um, hold on", puts me on hold, then comes back and says they dont work on AK's "because they can't tell if if's been illegally modified or not".
I say, "this isn't a mod, I need to permanently weld this thing on to make it nice and legal"
The guy says "It's not legal now?"
I say, "no, it's still in pieces, it's not done yet. This needs to be added so that will be legal when done"
The guy puts me on hold again, then a different guy comes on "Hello, we don't work on AKs because we can't tell if they've been illegally modified or not"
I tell him, "This is a kit, I'm building it up and adding the US parts to it, it's ok. I just need to permanently weld on the extension so it's nice and legal"
The guy responds" Well, no one will work on that kind of thing, because you can't tell if its been illegally modified or not, in fact i don't think any gunsmith around here will touch it. Some people think if you add 4 US parts and a US Hand grip, it's legal, but it's not"
Now this is flat out wrong, so I cut the guy off - "I've already added the 5 parts to it, that part's taken care of"
He responds "How do you know they're US parts?"
"Um, because "US" is stamped on the side of them when they were made?"
"That's not good enough, that doesn't mean anything"
Edited: I say "Ok, thanks anyway" and sign off. (this is not what I've heard from many other sources)