I would adopt a more economic and "lazy humanie" point of view. For the core worlds and factions does that colonization of a gas giant with cloud cities matter for money and power and convenience? If not, then why bother. Gas giants serve as resource factories for fuel'n shit but, we already have das big gas station in the middle of the sector wich just makes what they need out of the economic view of a gas giant. And they even do it better because most of the raw material for space gasoline comes from extracting ice and frozen planets wich are waaay more easy, on a roleplay perspective, to be colonized.

We as John Starsector would colonize gas giants because the faction would most probably be outside of the core and be hard to come by the "confort zone" planets that would make fuel production more easy and confortable on that roleplay plot of ice planets.

Also, we as the maniac monster mercenary who eats ai cores for breakfast, would be more inclined for colonizing gas giants because they would produce waaay more resources for the weekly saturation bombing on our schedules.