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.
Another reason why some people do that is because some of the members who start up threads use too much write up to fill up their post and some find it difficult or should I say boring to read the entire message but reply through the topic, take a good look at how short and simple your message is. You went straight to the main point.
Honestly you shouldn't blame those who write thousands of words before posting (not always necessary) they're trying to impress readers just to cause traffic on the thread and they forget that 89% of the users in the Forum don't like reading too much write up and sometimes it becomes pointless.
Off topics comes as a result of not getting the message coming from the OP, both the reader and the OP are guilty of this, desperation to get something can make members come up with off topics, like they have to meet up, get where others who came before you are like you want to rob shoulders with your seniors.