Computers (including consoles) have limited resources, at some point you need to deal with tradeoffs, for example do you prioritize graphics quality or do you prioritize FPS? Do you want/need to have more resources available for the physics engine? That eats on the maximum possible FPS. Do you want to do real time procedural generation? Do you want to use the GPU to run some kind of AI? All this are design considerations and there's no one size fits all prioritization decision for all videogames. Clearly the people working on Starfield believe that for their intended game experience graphic fidelity is more important than FPS, and this is a perfectly valid design choice even if you don't agree with it.