They're more like dummies, than fakes. I'd be highly impressed if someone managed to make a fake
CPU that actually worked! Would probably be worth more than the real thing, as a curiosity.
I'd say these packages have been carefully crafted just to be exactly the right weight, and appearance at a glance.
If the weight was wrong, someone working for the a distributor or shipping company might notice that a crate of them was too light.
Chances are someone has opened up a crate and done a switch, somewhere in the supply chain.