I've looked around a little bit and I can't seem to find much information regarding this question, however I am a bit curious - from what I gather all matches are 6v6 in NS2 competitive scene. Are there any differing size leagues/competitions/gathers?
Are there competitive 7v7 or 8v8 etc matches? If there are not, for what reasons exactly?
I think a competition tried (maybe it was Clanbase or some other generic website of the kind) allowing teams to choose between 6v6, 7v7 and 8v8. I guess it did not work.
NS1 was balanced around 6vs6 so that was it. NS2 may bit a little bit fairer because of the res system but would still probably give an edge to the Marines just due to how upgrades work and the melee versus distance concept. Plus, 6v6 is already hard enough to pull out sometimes in terms of availability of players so anything bigger really makes things exponentially harder.
Its derived from CS1.6's 5v5 + 1 for the comms. However, its become the standard for organizational reasons. Getting regular practices with a 6 player team is a nightmare. Adding even 1 or 2 players can make it totally unworkable.
I think it would be harder to achieve the kind if teamplay that makes comp NS great with team sizes above 6. That's not to say it would be less fun, just more random. And yes, organising 6 people to show up at a set time is already hard work for lots if teams I think, getting 8 people together would probably require a MUCH larger roster and that makes it even harder to achieve teamwork/synergy.
It's not derived from cs1.6. In NS1 you didn't have alien com. huhuh is right, clanbase hosted multiple leagues for 6v6,7v7 and 8v8. After couple of seasons only 6v6 stayed. As I remember, Americans continued to play both 6v6 and 7v7 for a while in their own league.
So it was 5m vs 6a on the field all the time. There is a great impact on game balance when you play 6v6 and 7v7 OR 8V8 matches!