What is the purpose of aliens coming to earth?

The purpose may be beyond our knowledge, but I also list a few:

1, come to earth for investigation. Some aliens will take some earthlings back for investigation, or they may lurk among earthlings.

2. Maybe aliens themselves exist on the earth, maybe not in this era, but in the first few eras of the earth. So they didn't come to the earth, but the survivors of the previous generation.

There are also opportunities to come to the earth for no reason.

It is also possible to occupy the earth as the planet where you live, but you find that human technology is still quite powerful, and you dare not for the time being.

5. It is also possible to prepare to invade the earth. Technology is far ahead of us, but the time has not yet come.

6. It may be communication, learning, exploration and self-development. Just as we earthlings know the outer universe.