The reasons, at least for me, were easy. You get the modularity of the AR platform, the power of the 7.62x39 cartridge, and the simple cool factor (much like having an AK platform in 5.56 NATO). As others have stated this has become my favorite platform to use, so much so that I assembled a 16" rifle with a side charger upper to go with the PSA 10.5" pistol I purchased from the factory. Both are a joy to shoot, though don’t expect 5.56 recoil, and I can’t tell you when I last took out an AR15 to shoot. There are so many ways to furnish, mod, and tinker with this platform to truly make one “yours”. They are a blast…BUT be aware that PSA has a lot of irons in the fire and product and part availability can be very spotty. There is availability right now, but that doesn’t guarantee there will be in a week, a month, or sometimes even longer. Expect major periods (read whenever there is a new product release, Dagger, JAKL, new AK gen) of time where parts availability will be scarce as PSA will be focused on everything but the KS platform… at least it will feel that way.
Overall, great platform and well worth the money, but be ready for possible frustration with supply.