If I were guessing, that is a demilled kit.
Which means, the trigger group is probably full auto and couldn't be used.
Besides, to be able to build one from a kit, you have to have a certain amount of US made parts, and Tapco makes a fantastic trigger group that is almost a match trigger, and counts towards us made parts where 922 compliance parts are concerned anyway.
Assembling an AR is a lot simpler than assembling an AK because you have to use a hydraulic press or jack for a lot of the AK parts. But there are many who like building their own. Again, Slade797 would be the guy that could answer your questions a lot better than I could. He's assembled several of them from kits.