Reverse Engineering

Hi,
Come to think of it, reverse engineering bid is quite interesting,as Now, Why can`t an F-16A/B be reverse engineererd, Airframe, Avoinces And Most of All Engine..Is that so hard to copy F-100-PW-220. You would have guess where I am taking this why not Paistan & China Togather tried to make a copy of F-16A/B version. Pakistan had it since 1983.
After all PRC did do to Mig-21F13, Tu-16s and Izrael copied Mirage 5 in shape of nesher. PRC & Pakistan Had F-16A/B .why didn`t F-16A/B get copied.Is that Hard to make a carbon copy.

On Engine if F100PW220 was copied, JF-17 wouldn`t have such a Lazyboy!

I need some info on this issue.?

Thankx

MiG_Master