Are you suggesting that the reason they aren't moving to a new venue is because getting their tickets sold out quickly makes them look good and the attendees feel special? As opposed to countless logistical concerns that come with organizing an event of this magnitude and importance?
I'll give you a moment to let the sheer stupidity of your suggestion sink in.
I'm not saying that it's the ONLY reason. I am saying that it is A reason.
OTOH, if you start getting the "wrong" type of attendees, the conference becomes less valuable for everyone. For instance, marketers who sign up just to network with the 5000 developers and don't bother going to a single session.
Why did they have so many tickets available back when it wasn't selling out, if this is such a good idea?