How does a polymorphic cryptor work and why sooner or later does a cryptor become unusable?

Question

C++ / C#

Describe the principles of operation of a polymorphic cryptor and why it will be "merge" sometime

Answer 1

For the same reason why the riddle "Without windows, without doors, the upper room is full of people" seems elementary to you.
Cryptography is solving riddles for a computer, and once solved, it ceases to be a riddle.

Answer 2

The code morphs, but it morphs badly. Then, after N the number of crypted stubs, you can stupidly select a common signature and always shut up this shit cryptor. Would such an explanation work?