I was the first to mention this, so let me explain.
There is certainly no shortage of activity on the thread. That is not the reason why it should be pinned (I mean, just because something is pinned doesn’t mean that it will be bustling 24/7, but I digress).
The entire point of General Discussion is to, well, have a general discussion. And the Time Wasting Thread is the epitome of just that. “This forum is for discussing practically anything on the site or off it, so long as it doesn’t belong in one of the other forums”? Replace forum with “thread” and you have a pretty tight idea of what our thread is all about. Additionally, it can serve as a pretty great entry point into the forum itself. We don’t bite.
TL;DR, Time Wasting embodies everything that General Discussion is and that’s why a pin makes sense.