Why is not everything that people have created is included in the cultural heritage?

Cultural heritage is those values ​​that are passed on from generation to generation. Values ​​must pass the test of time in order to become a cultural heritage.
Many values ​​of mass culture quickly become obsolete and are forgotten over time. For example, many pop works have been known for only a couple of years, and over time they lose their value for their fans. They understand that they “grew” out of it. Therefore, every work of culture cannot be made a cultural heritage. Likewise, films, paintings, books. They are not interesting to new readers and do not carry value or usefulness.