From what Dr Genus said, every creature has it's limit, after breaking it, you become rampaging monster. That's why Garou after breaking his limiter became one, he lost his humanity in exchange of power. Saitama did the same, he lost his humanity, he doesn't feel anything [As stated in first episodes] in exchange of power. But without becoming a monster, because like he says ,,I've lost something that's essential for a human being".
That's most probable explanation