system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass effect] Is there an in universe reason to why ships in the Mass Effect universe are smaller in comparison to other Science fiction series?

The largest ships in mass effect are the dreadnoughts which range from 800 meters to a kilometer. This seems large but when you compare it to the Punic-class supercarrier seen in Halo (4,000 meters longer) it just seems strange. Especially considering the tech level differences in these series. The mass effect universe seems far more advanced than other series and yet it's ships are a quarter the size. 

Obviously the universes are completely different but I would think with a mini cold war between the humans and the turians that they would just keep building ships larger and larger.
gpt
While you can get bigger, you also have to scale up the size of mass effect fields you have to create for them.  

Additionally, the drive cores make a lot of heat and build up a charge that can fry the crew if not discharged, and the rate of both scales with the size of the drive core, and past a certain point you end up where you are having to discharge even before making it between planets.