First of all, this is the only forum which is being used by the posters so often and there are so many threads and posts and posting never stops here.
I have no idea what that is supposed to mean or how it is relevant.
Google has less to do here, as all the crpto currency is here and people who invest in ICO are also from this forum, so thats why Bitcoin and altcoin dealing projects are advertise here as this is the only biggest platform for that.
Check out the site advertising stats here
https://bitcointalk.org/adrotate.php?adstatsThere is 5 times as much total traffic than there is coming from logged-in users.
From personal experience when I first got interested in Bitcoin in 2012 Google brought me here for anything and everything I wanted to know. I didn't actually join the forum until mid-2013. I also know that when I didn't use the forum for a couple of years that the referral link I left in my signature got about 5 clicks a day. That can only be because people were still finding the old posts I wrote back then, I'm pretty sure Google had something to do with that.