Because of the large amount of tea in China, and its value.

• Audio(General Australian):

  (file)

alltheteainChina (uncountable)

1. (idiomatic,hyperbolic) Something veryvaluable orpriceless.

   I wouldn't trade you away forall the tea in China.

   • 1986,William Shatner,Catherine Hicks, 1:07:18 from the start, inStar Trek IV: The Voyage Home‎^[1],Paramount Pictures,→OCLC:

     KIRK: Ha, ha, ha. Okay, the truth. I am from what, on your calendar, would be the late twenty-third century. I've come back in time to bring two humpback whales with me in an attempt to repopulate the species.
     GILLIAN: Well, why didn't you just say so? I mean, why all the coy disguises?
     KIRK: You want the details?
     GILLIAN: Oh! I wouldn't miss this forall the tea in China.

• all the gold in Fort Knox
• all the money in the world
• inte för allt smör i Småland (Swedish)

• price of tea in China