They tried ad nauseum to get rid of quitting from previous Halos and Bungie completely failed.
As soon as a map someone didn't like was picked, they would quit and unbalance the teams. Game of Invasion often turned into (virtual) massacres
as one team could easily dominate the map.
You'd sit there saying to yourself 'I won't be a quitter' and end up with a K/D of -50 because your only spawn points are completely surrounded.
Not fun.
The eventual quit ban itself was laughable anyway - some people have lives outside Halo, where they actually have to leave suddenly or their connection drops.
Drop-in Drop-out play is the way it should be - and needs to be.