Green tea is now popular in Japan.
As it was rare when 20 years ago, many 24/7 stores, supermarkets and vending machines sell cold canned and plastic-bottled green tea. When I was a child, we didn't drink cold green tea so often and only drink the hot one.
Now there are many 24/7 stores all over Japan and they sell a variety of boxed lunch, called bento in Japanese. Cold or hot green tea goes well with the lunches. So many people buy green tea, together with the lunch, at 24/7 stores for a lunch.
Plus, green tea is very healthy since it contains Vitamin C, catechin and so on.
By the way, I am surprised to hear that sugar is added to green tea to drink in some countries, but we don't add sugar into it.