I wonder if, prior to the world wars, green tea was more popular in the west. Is it possible that with the outbreak of anti-Japan thought that was so pervasive in the first half of the 20th century, green tea was rejected as being reflective of that culture? India was occupied by the English, so black teas might very well have taken over, and in a few generations, American and English folks forgot - or had erased - their knowledge of green teas. I'm curious if green tea's popularity was altered by world events. It seems emminently possible.
This last holiday season, I was going to get a good green tea for my little sister (a very normal American), and Yuki said to me "That's not a good idea. Most people don't know how to make it." So true! The fact that people here are even bringing bags into the talk - that would be like asking about Beef Bourganiase and equating it with a can of Dinty Moore. They're both beef, but very very different beyond that. Green tea takes a fair amount of practice to brew properly. It takes a fair amount of thought, also, not just 'wait for a few minutes and then drink'. The amount brewed has to be just enough, the water temperature has to be just right, and the timing has to be observed. It's not difficult, but it does take time and attention. That alone makes it almost incompatible with a typical Westerner's view of tea. Of any beverage drinking, actually. Again, none of this is difficult, just different. Ingredients matter, and some practice is required.
And, as cynical as it might be, anything which requires voluntary attention and practice will be doomed to mass unpopularity in the west.