Have anyone noticed that the reason why some persons post go off the topic is because they don't read the entire op writing before they reply to a thread, some persons respond to a thread based on the caution of the topic and that is why we meet up different opinions or suggestions that is not in lines what the OP points of view.
Secondly, when someone have written what you want to write in same thread you have to give off, instead of making a pointless point, I know very well that many users in forum make off topic because what I outlined.
You can also discover that after a person makes an off topic post of which he has no idea on the subject matter in consideration, the experienced members correct such user and he also feels bad and the next think you will deduce is from the perception of being bullied by the old members, you can imagine that if everyone of us are posting off topic, the entire forum will just be full of spammers, that is why each boards has its own area of discussion as the case may applies to what we can be able to contribute over there.