I visited your post history and I see that there's nothing wrong with it (IMO) so I don't think that poor quality of post is the main reason why you are experiencing this.
There's a big chance that other respondents are right, the thread where you posted was deleted that's why your post count is declining. But don't worry too much because this is not an unusual case, it is normal and I'm sure that others (including me) already experienced the same thing
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This kind of scenario is inevitable because cleaning the forum is a part of mod's duties but you can lessen the probability of experiencing this at least. Only post on threads which have are decent and have a sense as well, and prohibit yourself to post on spammy, shitty and mega threads.