I can give you a concrete counterexample to that. The Perserverance rover is carrying an entire experiment (MOXIE, which makes oxygen from CO2) whose only purpose is to serve a future human mission. NASA is encouraging more of this stuff, and it means automated Mars rovers will go to the boring sites that we need to prep rather than look at the phenomena of highest scientific interest on Mars.

That said, I'd love to hear what people who work at JPL and NASA have to say to your point.