If my post is considered spam or junk post then there must be dozen of other post in the same thread that must be deleted because they don't meet the standards.
That's probably true, but there's only so much reporting that can get done and so many posts looked at and deleted by the moderators for any given thread--remember, new threads are popping up all the time, either new ones or ones that got bumped and many of them are filled with garbage posts. So what you're asking is "why me?" and there's no great answer for that other than either someone noticed your post(s) in particular or your posts were much worse than the others in the thread(s) involved.
Either way, you probably won't get an answer from the mods and even if you do there's nothing you can do about it except to take this as a warning. Hell, I've had plenty of posts deleted by the mods and I haven't bitched about any of them. And I'd say that most members who make a decent number of posts have had at least a few of them nuked--so don't take it personally and just try to do better in the future.