There is no reason on the side bar other than not wanting it to be longer and unwieldy. There isn't much horizontal space there. It could probably benefit from a new layout of some kind in the future for sure.
There is reason on those submission pages. Most of them pull from the submission tables which only have data fields common to submissions of all site sections. They don't delve into the individual sectional data (which the game a hack is for is). It's very efficient and simple this way. I have experimented with doing the whole thing differently with new infrastructure, but I have not been happy with the results. Complexity and resource utilization goes way up. It is an area of the site that will be worked on as more significant infrastructure changes are made heading toward RHDN 3.0, but like all of my projects, it takes a long time to get there with such limited free time.