I don't consider myself an AA'er at all, though I have tried to "work" the program and have attended at least a couple hundered AA/NA meetings over the last 5 or so years.
My understanding of why people with longtern sobriety "keep coming back" is to give back to the newcommer, which in turn "helps" the longtimer. I believe that is kinda the jist of Step 12. Most, but certainly not all, people I've known with longterm sobriety do not necessarily attend meetings every day. Many go once or twice a week, usually to their "home group" to keep in touch and do service work. That is not to say they don't beniffit in other ways by continuing to go to meetings, but many people find that as their lives become more "normal" (whatever that is!!) work and family obgilations that had been avoided while using and in early recovery take up more of their time. Again these are just my observations. I am by no means an expert. Take care.