To exactly answer that question... I dunno. I can only assume it's just sensitivity, since clearly people don't like being ignored and sometimes would rather be told what was wrong rather than be blocked. Now if they're obviously trying to annoy you even when you tell them to stop... That would be /kinda/ immature of them, and is exactly what the block button is used for to be honest. Likely it will help them learn not to by then, but I think respect is important.
I don't want to seem like a know-it-all but just a thought on this subject. You know what I'm trying to say, at least?