Three parts to this question:
这个问题有三部分：
Why is the cost structure of Starbucks high;
为什么星巴克这么贵；
Why are they able to charge such high prices;
为什么星巴克可以这么贵；
And why do they choose to charge such high prices?
为什么星巴克要这么贵？
Regarding the cost structure, as others have pointed out, they have a high cost model for producing coffee beverages (and other products).
说到成本结构，像其他人指出的一样，在他们的咖啡制造商业模型中很高的成本（他们也生产其他产品）。
Principally, they are often located in high rent areas, and are optimized for service quality rather than cost-efficiency.
主要来讲，它们经常开在租金很高的地段，而且使服务水平最佳化，而不是追求成本效益。

Regarding how they are able to charge such high prices, it's largely a product of branding and convenience.
说到他们怎么能要价这么高，很大程度上是因为这集品牌和便利于一身的产品。
Though I wouldn't say they are out of line with other independent coffee shops, so the branding perhaps isn't even that marginally important, other than attracting customer volume.
虽然我不会说他们和其他非连锁咖啡店有多不一样，所以最重要的是吸引消费者，相比之下品牌不是那么重要了。
Regarding why they choose to charge such high prices ... because they can.
至于为什么他们选择要价这么高..因为他们可以要得这么高。