Well, let me explain it like this:
When I'm able to post on GAF I'm much more likely to waste many hours of my day on there (like 7 to 8 hours). Plus, it splits my attention so I can't devote my full focus on my homework or design projects.
As for posting on The Bore, I only waste maybe a total of 2 or 3 hours on here because it's a smaller community and there isn't a whole bunch of topics being updated with new posts all of the time.
And I do lurk on GAF but it's only for a couple of minutes just to see if someone posted something interesting in the few threads that I'm currently following.