From what I've seen and heard from some fans, it's the rules. I'd say Production Car racing is the equivalent of Group Aand that's growing massively, even with owners spending big dollars in development. GT4 would be akin to Group C. Super Touring(wasn't received well here) would be TCR. The series would have been the same without Penske. Some of best racing, before Penske, was with the change to COTF.
Racing being good isn't a factor in a massive manufacture joining the series to win races potentially championships and use it as a means to sell a brand through Motorsports achievement. While the change is good, for the fans how does it actually represent manufactures? That's the question that should be asked.
COTF rules were too inconsistent. DOHC engines, drive by wire, etc, but Ford and Holden didn't want to change. Had they led by example, I believe it would have been easier for manufacturers to want to come in(regardless of budget). The restriction on the amount of manufacturers was dumb. Why set a maximum of 5 or 6? Clearly that shuts most out. Making an excuse because it would be tough to manage, requires a smart team to manage it.
Technically one of them is leading when another certain group could of. It's confusing to me that Nissan wouldn't shift over to a formula they're more use to winning with, and would instead opt to stick with V8s, while Holden actually does the V6 tt thing. Also remember yet again VASC was the issue on this, the rules barely came into effect to use such engines, and so Holden moved as fast as they could on it. I suspect had Holden not switched to RBRA, they wouldn't have had the means to develop the engine in a way they feel it would be competitive for Supercars, even if it's a proven formula from PWC. If the rules for the COTF actually synced together or even staggered a year, rather than come in 5 years after the initial understanding in 2012, and didn't try to pander to old men with V8 nostalgia, perhaps more groups would have got on board and still be here.
Manufacturers saying, "it's not for us", means the series isn't open to listen, let alone willing to change. Now the series is here. People that can see the racing say it's a tough series. Close racing. Management try to court manufacturers by waving multiple doors and engines. That's desperation from the show promoters.
Ford being so off and on in Australian racing, is a mystery. To have multiple Touring car & loyal (V8)Supercars teams, win championships with the blue oval/Ford body and Ford to throw those relationships in the bin, is the thing that bites. Again, from what I've seen/see.
Perhaps it's the series isn't open to listen, perhaps it's the fact that VASC refuses to be anything but international other than in name, perhaps it's because the mainstay teams have to much power to make a new manufacture feel it's not worth the effort. Or it's a bit of everything. Fans at some point (those who have a direct influence) have to decide at some point, to either try and see VASC survive another 20 years through modern changes other series are going through.
As for Ford, it's business, great job to teams like PRA(Tickford Racing) and DJTPR but why should Ford come back to a regional series in a region they lost heavy in. The money losses for them didn't help and even if there is a great loyalty it wasn't all that reflective. Due to that, I can see why another manufacture would say "why am I going to join this group, race, win, and then not see a sales take over or domination in the region for our brand?"