I chalk this up to primary two reasons. First, I cared a lot more about the implementation details of the C program than I did the Python one, and second, it's just better at simple stand-alone python programs than it is at C programs.
The criteria I know use is "do I care about the implementation details of this?". If I do (because for example it's going to be long-term code that I need to maintain) then the agent likely isn't worth it. But if I don't, there are huge efficiency gains to be had using the agent.