If its the overall data of the forum then the big reason is in halving people are making money, so they are posting less and reading more, another reason is, that obfuscating the site's advertising is banned on BTT so there are fewer members in campaigns so fewer posts are being made plus current running campaigns require less post count I assume. Besides these reasons, I don't know of any other. But overall its not a good thing.

Yeah another reason could be some people are spending there time on ALTT now, As I am spending more time there then here I assume, as I am newbie there (by experience but trying to catch things up as I am senior here hehe). Overall, we will see the same number of traffic post wise soon when more comapings will be running.