There are billions of people who speak different languages ​​(or different English), but they learn Standard English so they can communicate with more people. There are also many other languages ​​that come close to the popularity of Standard English, so they should be just as valuable. Amy Tan's mother learned Standard English so that she could communicate with the people around her: as most of the people she knew spoke Standard English. When my family came to the United States we were not forced to learn English but it was practical to learn it (but we could still talk to many people in the United States without knowing English). The reason we learned it is the same reason Amy Tan and her mother learned it: to communicate with a broader audience. Most people learn Standard English to broaden the groups of people they can talk to