There are sportive riders and potential sportive riders who do not realise they would *love* Audax. Why on earth wouldn't we tempt them with a full TLC ride?
I think the pool of sportive riders that would get and *love* Audax is smaller than you think.
Sure there are plenty of people that currently ride sportives that would be happy riding an Audax for a change of pace but discussing this with riders from my local club the main draw of sportives are:-
* routes shown clearly shown on the website with outline maps or links to GPX files and exact elevation figures
* fast pace (including being able to average >30kph) and the sense that it is kind of a race
* food stops (energy bars/gels, bananas, drinks) at the side of the road (they don't want to have to get off and leave their bikes while they go into a scout hut or village hall)
* electronic timing/validation with finish times published on a website (along with gold/silver/bronze time categories)
* large fields of riders
Some of those are just incompatible with Audax by definition.
We've seen that rides that put effort into marketing have had some large turnouts or quickly fill up. Ditchling Devil, the KWAC rides, some of the Bristol rides,
Severn Across London-Wales-London. It's amazing what a rebranding, a separate flashy website, and spreading it around local cycling clubs can do for popularity.
But you can't escape the fact that many Sportive riders just want a route to follow, have access to some easy to grab assistance (roadside stops, not TLC for rides of 200km or less) and to effectively be able to ride non-stop (as in not having to dismount their bike, they may stop at the refuelling stops). The concept of a routesheet and a Brevet Card are a complete anathema to them. (I've said it elsewhere but I'd be surprised if in 5 years AUK isn't offering validation for calendar events by GPX tracklog - just like you can do for DIYxGPS now. You can even take away the manual job of uploading it to AUK for validation: Enter a ride, link your Strava/GarminConnect/etc account if you haven't already, ride, upload, AUK scrapes the Strava link and validation is automatic if the route is followed closely enough.)
The main AUK website redesign may sort a lot of the marketing/presentation side out, especially if the existing information (elevation, route, etc) is presented up front (many people are unaware that there are GPX files hidden inside a zip file link on the calendar event page).