It is not always a people group's choice to stop speaking their language as assimilating to the majority language is often out of political or economic necessity. For example, the U.S. has a strong, monolingual English culture; society pressures and expects immigrants to speak English. In the late 19th and 20th centuries, the U.S. government built Native American boarding schools where Native American children were forcefully assimilated into European-American culture. Speaking their native language was disallowed.
Today, many indigenous North American languages are endangered or extinct.
The depleted number of Indigenous North American languages is an example of how a ruling government suppressed a people's group's language through forced assimilation.
Parents may choose to raise their children in the majority language and not teach the minority language. Yet, children may grow up and feel a loss of cultural connection or a missed opportunity in not learning their heritage language.
Just because the parents do not find the minority/endangered language valuable does not mean the language itself does not have value to their children.