Factual error: Science Officer Tilly calls the planet Trill a "very big" planet. It has an area of 500 million square kilometers. But that is not so large a planet. The Earth has an area of 510,100,000 square kilometers. So Trill is slightly smaller than Earth. Not really a "very big" planet.
The War Without, the War Within - S1-E14
Other mistake: In dialogue, Starbase 1 is described as "100 AU from Earth," which is over three times the orbital distance of Neptune, but still within the Solar System. But the onscreen graphic shows the starbase next to a planet that can be visually recognized as Earth; portions of North America, including the Florida peninsula and the Gulf of St. Lawrence, are visible.
Answer: Perhaps they didn't want to take the risk that Control - a tactical and strategic analysis program - would choose to place its entire core programming into a single fragile human body (Leland), despite previously demonstrating the ability to decentralise, duplicate and transfer itself to numerous computer, cybernetic and organic systems. If any trace of the Control program still existed, it could make another attempt to seize the sphere data.
Sierra1 ★