First off habitable planets play a major role in this setting. Furthermore this is a setting whose elements somewhat require that the surface of planets are not soft targets.
In particular planets are defended not just by laser satellites and surface to orbit missiles, but also by umbrella shield generators that protect cities and fortifications in particular.
However I run into a major issue where the importance of planets becomes difficult to justify because the shields that somehow can defend entire planet bound cities could similarly be used on space stations or larger space ships.
The exact nature of the fields I'm still toying around with as well.
The closest handwavium candidate I have is something that interacts with a planet's gravity well. Which makes the explanation something to the effect of 'Something something, gravity well, something to do with gravitational gradients, and something to do with flat space and curved space
However, while I can't be sure, I get the feeling it's a bit of a sloppy justification, in particular I can't even articulate what the shield is even doing in the first place and therefore leaves the potential for holes I might not be prepared for.
So what pseudo-plausible but consistent handwavium could I use to explain why shields that planets use in defense, are strangely more practical in operating on the surface of planets than other environments?