When the aliens were trying to build their machine, they finally tried to establish the way to correspond to earth. After two millennials, they established the way to communicate and correspond to the people of earth.
When they found the green signal, they immediately arrived and tried to do research and development on how humans have developed their culture and communication.
This way, they were trying to establish a peaceful channel and try not to engage in any sort of miscommunication.
This is why the correspondence was important and when it was established, a peaceful channel was also created for different species to prosper together in different planets.
Image is my own.