Resources

Same thing every colonizer wants, resources. This may be in iron, wood, slaves/employees....just resources of any kind. Maybe just clean air and water. Tourism is a possibility too. Earth's people/corporations will have some scarcity that they don't or can't get from Earth (or the solar system). To satisfy that demand, they will naturally go exploring in the colony.

Unless Earth of 21XX is significantly different than 202X, capitalism will still exist. All those capitalists back on Earth will have lots of money to spend and a burning desire for returns. A brand new unexploited land will be soon be swarming with prospectors of all types.

The bargaining position of the colony is weak. Their force of arms will be limited to pre-industrial weapons which will do exactly zero against orbital bombardments. They will take whatever terms the Earth based forces are willing to give them. For resources, the strong will always prey on the weak and they will rationalize however they can to make it okay.

We see this pattern of exploitation over and over and over again. The English, Spanish and French when colonizing the Americas. What Japan did to China in WW2. What the US continues to do to the Third World. So, unless there's some kind of enlightment that clamps way way down on capitalism as we know it now, that newly discovered colony is going to be really unhappy.