The answer to this is very simple. Why did you not report any of his posts before this?

In the last 6 months, only one of his posts was reported, and even that was not a serious post warranting a suspension.

We are not able to act and monitor each and every post made by members. If you see a post that is breaking board rules, report it so that it is brought to the attention of the moderators, and we will act on it.

p/s action has already been taken on the above mentioned account.