They don't really "copy" Glock, they ride the marketing wave for striker-fired-safetyless guns masterfully created by Glock. If you take note, there are no real "Glock clones" out there, to the contrary: everybody is selling something that they think addresses one shortcoming or the other of the self-appointed "perfect" 2"x4".
People have "just copied" the 1911, more than 80 manufacturers. And the CZ 75. And S&W revolvers, and Colt revolvers. And others. But Glock? Apparently it's not so perfect that people just want to copy it... They're interested in copying the sales, yes and double yes, but not the graceful lines and creaking trigger...