There are several reasons why there have been no human missions to the moon since the Apollo landings. Some of these reasons include:

1. High cost: One of the major reasons why there have been no missions to the moon is the high cost involved. The Apollo program cost an estimated $25 billion (in 1973 dollars) to send 24 astronauts to the moon. This was a significant investment for the US government at the time, and it is unlikely that any government or private organization would be willing to invest such a large amount of money today.

2. Lack of political will: Another reason why there have been no missions to the moon is the lack of political will. The Apollo program was driven by the Cold War and the desire to demonstrate US technological superiority over the Soviet Union. Today, there is no such political motivation to send humans to the moon.

3. Focus on other priorities: Governments and private organizations have other priorities that they consider more important than sending humans to the moon. For example, NASA has focused on developing the International Space Station (ISS) and exploring other parts of the solar system, such as Mars.

4. Technological challenges: Sending humans to the moon is a technologically challenging task that requires significant investment in research and development. While there have been advances in technology since the Apollo era, there are still many technical challenges that need to be overcome before humans can safely travel to the moon and back.

5. Risk: Sending humans to the moon is a risky endeavor. The Apollo program had several close calls and tragedies, including the Apollo 1 fire that killed three astronauts. Today, there is a greater emphasis on safety and risk mitigation, which would make it more difficult to undertake a mission to the moon.

Overall, there are several reasons why there have been no missions to the moon since the Apollo era. While there is renewed interest in returning to the moon, it remains to be seen whether governments and private organizations will be willing to invest the necessary resources to make it happen.