They weren't the only ones with the idea, just the best at it. Many other pairs had formed, and some full fighting parties, with tanks, casters, and a healer. Since they didn't know the way the game's scaling was balanced yet, letting rotating members get the last hit for the points seemed to be a good way to get everyone powered up.
Many of them had forgotten that the announcer told them that the game rewarded innovation and difficulty more highly, so the gains they were getting by just taking the last hit on a disabled opponent weren't nearly as high as they would get in a hard fight. The two-person teams were doing better since the fights were more even, but the solo players were getting quite a bit when they could overcome a pair.
Nico and Max working together were making up for the lack of bonus in the pure volume of kills. Every few seconds, one name or the other would light up the screen after they abandoned the edge of the forest to go hunting.