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.
One thing I’ve come to realize in the forum is that, we all have our ways of reasons and different opinions about a particular subject matter and at every case scenario, I always try to see reasons with what people are thing to say.
Personally, I think one major reason a post can be deleted by a moderator is if the post is most a one line off topic post or a one word comment which didn’t making a many meaningful contributions to the very subject matter.
At some point, you also have to realize that, here is a forum and a community with diversed opinions and group of persons with different languages and cultures and there are people who English isn’t there official language and you shouldn’t expect such persons express themselves same way with someone who is already proficient in English does.
In conclusion, post are mostly deleted my moderators if they don’t meet a certain criteria.