When you say “I wouldn't do it for all the tea in China!” you are talking about every single leaf of tea in the entire country of China. That's a lot of tea.
When you talk about all of one thing, you mean the whole thing. When Shakespeare writes, in As You Like It, “All the world's a stage,” he means the whole world. When I ask, “Did you eat all of the pie?” I mean, “Is there a piece left for me?”. If you are "all upset" about something, you are very upset; what's upset you has got a hold of you. Would some pie cheer you up?