There's very little _scientific_ motivation to send humans to do science instead of robots. Robots don't need to eat or drink (much more efficient payloads) and don't expect to survive the mission.
The motivations to send humans to other bodies at this time are political; to prove who is and isn't a superpower of the 21st century.
The motivations to send humans to other bodies at this time are political; to prove who is and isn't a superpower of the 21st century.