Well, finding stable lifeforms is a nontrivial problem, assuming GP is somewhat faithful to biological evolution.
The earth has only existed ~1e9 years. Assuming some finite average number of "computational ops per year", the number of possible dna strands quickly exceeds the total computational capacity of the planet since its birth.
In any case this is beside the point. The fact remains that genetic programming is a class of algorithms that has not been succesful in the slightest. People should just stop talking about it as if it was anything other than a complete failure, since that will only lead to even more wasted human effort. Gradient descent on the other hand is hugely succesful in solving a wide variety of real problems.