The racing is usually rubbish, but let's give it a chance with the hilltop finish as it might make it a bit more than a Bonus Seconds Extravaganza. The UCI points available for it are ridiculous given the stages average 130km with no climbs, but it is what it is.
Ultimately, it's an easy race that people go to for a bit of fun. Biker jk comments on it being easy because the Europeans can't handle a harder race at that point, but that's only half right. There are plenty of Europeans who can, and do. But a lot of the bigger names don't, and a lot of the Australian big names come from a track background, so sprinting is a-ok with them (Evans is obviously a huge, glaring exception). At the moment, it's quite simple: people who want to do climbing in January go to Argentina, people who don't go to Adelaide.
The Tour de San Luís is a much better, more entertaining and interesting race with a really intriguing field. But the Tour Down Under has more big names, and World Tour status. It's down to what you want. The Aussie fans on the roadside probably would rather see the stars. The riders are happy to roll around and let the sprinters have their fun. I don't see the problem, other than that neither race are really given adequate coverage.