alt Hacker NewsI've never seen this either. I'm just interpreting what I think OP meant.
I used to live in Seoul, and new special food or drink items definitely would cause fad waves and would appear on Instagram feeds (Seoul is notorious for this), but I doubt it was the major parts of Starbucks' business.
The sweet latte-based drinks are a huge part of Starbuck’s business. They make far more money on these things (and frappucinos and iced lattes, etc.) than coffee or espresso. But it’s mostly just selling them to people who like the taste (and don’t really care for plain coffee at all). The people posing for instagram are a small minority.