Because the Tanfoglio departure from the original design is in many ways superior. The Tanfoglio firing pin block is superior to CZ's and was introduce first (theirs lowers the block, reducing spring pressure while CZ's rises the block, increasing pressure, the result is the Tanfoglio design will always have an advantage in trigger quality out the gate). Also, the Tanfoglio safety allows for cocked-and-locked, hammer down with safety off, or hammer down with safety on. The CZ design only allows the safety to be engaged with the hammer back. The Tanfoglio design also does without the CZ magazine brake, which is superfluous at best.
Now, CZ does still hold a firm place in my heart in 9mm, but the reality is that the Tanfoglio design improvements are actually superior to the original CZ design. One can argue execution and I'll grant CZ quality is superb, but design is solidly in Tanfoglio's corner. The proof of this is that every CZ-based design, save for early 1980's copies like the early AT-84, is based on the Tanfoglio improvements (even when they do not use Tanfoglio-made parts such as Sarsilmaz and ASAI).
