title_body: Why isn't coffee commonly sold in sachets, like tea bags?
upvoted_answer: As a matter of fact, coffee is "commonly" sold in some kind of sachets.
  
  In Japan, there is what is called "one-drip bag coffee". It consists of a flat sachet that you can unfold to deploy a small scaffold. The scaffold adapts to any mug-like cups. It unveils a filter containing ground coffee, as it unfolds. You just need to pour hot water in the filter to get a decent cup of coffee.
  
  I will not link to any maker or brand, but most coffee dealers in Japan offer these bags---pretty convenient and offering a decent cup for the price. These bags seem somewhat popular in Japan.
  
  I am not sure about global availability, though. Several countries do not sell them (e.g. Europe, perhaps because of the French / Italian influences).