The following is my opinion and was written without any research done:
The Supra has a few marks against it. First, it doesn't have the pristige of being a 'legendary' car, like most fabled 'pony cars', ect. It's not old enough yet to really be considered collectable and it didn't do anything really "great" for motor sports. Come to think of it, neither has Toyota. Don't get me wrong, but I don't really recall any great achievements Toyota has done in motorsports.
Ferrari? They always win F1. Mazda made the 787B, which dominated Lemans once and caused them to ban rotarys. Audi made the Quattro which crushed rally for several years until other automakers could compete. Ford made the GT40 which raped everyone at Lemans for a few seasons... the list goes on for motor sport achievements... but I'd have to try to find one for Toyota. I honestly don't know of any great achievements Toyota's made off the top of my head. Winning a couple of races isn't setting a milestone, changing the way races are won is, imho.
Thusly, I present that Toyota has a lack of pristige about its name.
The lack of pristige around Toyota, to it's detriment, causes it to be snubbed when considered as a 'classic' car maker: someone says Jag and people go "oooo" "ahhhh". But, any decent enthusiest knows they have a bad habit of falling apart at inopprotune moments. Mercades? Same thing. All Top Gear does is harp on how poorly built Benz's are... stereotypes exist for a reason: they're generally true. Pony cars are written into history by some truely great hollywood movies, and they'll remain there for a long, long time: coveted. Were they actually great cars? Not really... hardly spectacular compared to cars today in terms of performance, even modified to the teeth.
People say Jaguar and they think luxury. People say Ferrari and they think fast, lamborgini: glamour and status. Porsche: Status and fast. Ford Mustang: classic and iconic. Land Rover: Goes over anything anywhere. Land Cruiser: isn't it Land Rover?
People say Toyota and they think reliable family car. You don't get a collectable car from a name that implies reliable family car.
My point is that you cannot engineer passion into a car. What makes a collectable car is not a quatifiable, measurable element hidden somewhere on the chassis. It's the subjective 'spirit' that the car has, something great that it did. Most of the truely classic cars that are cemented icons in society changed the way that automobiles are designed, manufactured, driven, or raced.
Being a great car is not enough.