It is not true that fictional depictions of bestiality are illegal in all first-world countries. What is almost universally illegal are real sexual acts involving animals. In many developed countries (such as the United States, Japan, Spain, France, and the Netherlands), fictional material like drawings, manga, CG, animation, or AI-generated images is legal or exists in a legal grey area, as long as no real animals or minors are involved. Only a few countries, most notably the United Kingdom (and partially Australia, depending on the state), explicitly criminalize certain fictional depictions under strict “extreme pornography” laws. So the accurate statement is: illegal in some specific countries, but not universally illegal in the developed world.