Nomad On CS GO competitive match you need to win 16 rounds. 8 it's for casual game, a non-sense mode game. (economy ruined, only one side played, too many players (8 or 10) on maps designed to be played in 5 against 5, no team vocal, etc...)
You cannot even train CS GO on this mode... I never understood their purpose with this mode.
If you play competitive games, like CS GO, LoL, Starcraft 2, etc... all games last long enough (about 30 minutes more or less) and this is normal. You must give the dominated team time to be able to come back, to think about strategies, not to mention the evolution of the economy or xp, etc ... In 5 or 10 minutes (or 5 rounds to win), you wouldn't have time to include all of that so it wouldn't be a competitive mode.