For me it's about performance, cost, design and materials. E.g a car built with carbon fibre is obviously going to be the "premium" choice over a car made with other materials, which also effects cost. This will probably also make it a hell of a lot more exclusive, and will likely be made be a high end and already "premium" brand. So they're all tied closely together.
Although you mention styling is very subjective, which I agree with, I do think it has something to do with making a car appear "premium". Even though it may not add much in terms of performance and won't effect the technologies within the vehicle, the styling definitely factors into whether or not the car is heavily sought after imo.
Think of it like beauty standards outside of the automotive industry: beauty is most definitely subjective to each and every person, yet some individuals are highly regarded as being "beautiful" or "good-looking" because they tick so many people's boxes of what looks good.