The "I'm busy" excuse is kind of like "It's not you, it's me."
I agree with you (!!!) that in spite of inviting many quality posters, they post for a little while, and then find their way back to GAF. Then people offer excuses (Oh, he's just busy and only has time to post on one forum. He will come back, you'll see!) but they never come back, save for a few days here and there, and then go right back.
EB at this point isn't the exclusive club a lot of people here believe. Most people who have spent a few hours in the OT know about the board. The Borecast is the best part of the site TBH and you can keep up with that on GAF.
Just my opinion.