Assuming it's all stock, and boy I have to say there's little doubt in my mind, check out the cable housing for the rear derailleur cable. It's like 2 inches short, at least. Probably shipped that way, and the shop, nor the assembler either one, likely gave a shit. Hehe.
The ol' Shimano Deore-ish rear derailleur. Really not a bad piece, just heavy.