A thing that feels kind of obvious, but I think genuinely confuses a whole lot of people in the moment:
When somebody posts something in their TL, unless explicitly stated otherwise, they’re not talking to •you•. They’re not implying it’s relevant to •you•. They’re not specifically looking for •your• thoughts. If there’s a question, it’s not addressed to •you•. They’re just talking.
If you reply, however, you •are• talking to them.
Different situations. Different appropriate social forms.