Well thats the thing, maybe just the women have become sterile, maybe most of the men are. I have no idea, it has been clear that him having a viable heir is an important part to the taking over Earth plan. It would make sense by how interested the other Viltrumites were that he had a viable heir. They have become mostly sterile as a species and they have refocused to conquering worlds that could be used to continue their race.
Well thats the thing, maybe just the women have become sterile, maybe most of the men are. I have no idea, it has been clear that him having a viable heir is an important part to the taking over Earth plan. It would make sense by how interested the other Viltrumites were that he had a viable heir. They have become mostly sterile as a species and they have refocused to conquering worlds that could be used to continue their race.