Its not boils, its has to do with the range of the weapons and the lack of engines on a starbase. When ships battle, they do so in the same square, more or less. Distance is a bit warped in the game, but each square inside a solar system is light days across, and outside a solar system, light years across. Unless the base can close the gap, which is the no engine problem, it couldn't reasonably bring weapons to bear vs. ships that didn't choose to engage.
Now, how can military starbases impact fleet battles light years away with lasers, missiles, shields, etc? Makes no real world sense, but its a gameplay rule.
Really, sensors and strategy in this game disregard the speed of light as an unbreakable rule. There is some method or kind of warp drive sensors, radios, influence transmitters, etc. that allows realtime sensing, reporting and response across light years. I have no issue with this problem because the game would be unplayable as is if it was restricted by physics as we know it.
So in my circuitous and maybe irrelevant logic, I have said that they don't do it because it doesn't make realistic sense, but the rest of the game doesn't necessarily make realistic sense either, so back to your original question, why not? No idea. Good question but I like the mechanics as they are.
Not sure I helped any here, but I can't resist posting this mess anyways.
