https://en.wikipedia.org/wiki/V%C3%A4tternrundan is the classic example of how big a single (long) event can be.
18,000+ finishers of the 300km route (and ~80% of them Swedish so it's not just a huge influx of tourists).
One of the things I like about Audax is that I can choose how to ride it. Some I ride with minimal stops and minimal human contact in order to get round quickly, and some I'll ride in a far more social manner.
The more I've done the less I seem to care about the TLC available, but I'm very grateful for the TLC when I was starting out as it certainly made the difference on a couple of rides.
[EDIT] Also, what I carry has changed drastically over the years mostly due to my changing attitude to risk and reward. When I first started riding Audaxes I wanted to complete the ride at all costs, so I carried spares for ridiculous things that could have gone wrong, I didn't want to DNF due to mechanical. Now I'm not bothered (to the point of not being worried too much about validation[1]), if something goes wrong that I can't fix with a standard toolkit (assistance from others on the road) and/or some ingenuity then I'll accept it and make my way home somehow. I may now look like a "sportive rider" because I'll use a small seatpack on a 400km ride but this doesn't mean I'm any less self-sufficient - preventative maintenance and experience has allowed me to stop carrying as much stuff.
I personally think the biggest barrier to greater adoption of Audax is the concept of routesheets and Brevet cards. Sure there are GPX files available for many events, but you won't see a big uptake in Audax until there's some form of electronic validation (be it from chip timing or GPX submission or Strava account linking). Being able to satisfy the traditionalists (who want to keep their Brevet cards) and the modern generations is the key.
1. I chose to DNF one ride about 2km from the finish because finishing it would have meant missing the hourly train back home. I gave the cards to a rider going past and asked them to let the organiser know - my card was returned to me validated. (The ride was slightly overdistance and I had ridden 75km to get to the start.)