It's not a real problem on Stack Overflow. Because Stack Overflow isn't just a forum, it's supposed to be a repository for reference. Let's examine a hypothetical:

Newbie programmer Tim submits a question on Stack Overflow. "How do I deserialise a JSON in C?" An answerer replies "that doesn't make any sense. What are you actually trying to do?" Tim explains that he's trying to make two parts of his program communicate, and he heard some out of context advice that a JSON is a good way to do it. The answerer helps Tim out by explaining a better solution to the problem.

A year later, professional programmer Mark googles "how to deserialise a JSON in C". Mark's client wants to pass JSON data from a web application into a C program they bought, and they don't care whether it's good practice. Mark understands this situation isn't good practice, and he suggested a better tool, but the client doesn't care because they spent a lot of money on this licence and using a different tool would make them look like fools. Mark isn't happy, but he's going to try his best.

Mark finds the stack overflow thread created by Tim, and it's completely useless. Nobody actually answered the question that Tim asked. Tim is happy because Tim's individual problem was solved. But Stack Overflow isn't any help to Mark, or the hundred people like him who were also put in an unreasonable situation by their bosses and clients. By helping Tim, the answerer frustrated everyone else.