They are in China, where Copyright enforcement isn't that strict on Chinese companies copying non-Chinese products. Anyways, Lego lost a legal case recently protecting their brick design, and technically it doesn't say "Optimus Prime" and it doesn't have an Autobot symbol... so Hasbro can't say much about some red and blue block robot.
Still, if Hasbro and Lego got together and released the "real thing" with this design in the US for about $25-30, I bet it would sell. They should do the fair thing and copy the design from Kazi right back!
I don't know if official Lego Transformers would be as good as these. Most licensed Lego products seem to have a lot pre-made parts, requiring little assembly.
It really seems like Hasbro sets are getting more and more dumbed down.