If they don’t reproduce where do they come from , and why can’t we eradicate all of them?
They cause other things to make copies of them. As for eradicating all of them, it’s simple: Just comb every square nanometer of the Earth, and destroy them all. So long as a single copy remains, it might infect one creature or another, and make billions and trillions of copies again. Good luck finding all of them! (Don’t forget to search all the seawater, too.)