When will the stupid meme die? 1v1 and 2v2 have been the most competitive and fun game modes to play and watch since CoH1. There isn't a single RTS in the universe were people give a shit about 3v3 and 4v4.
1- Not since Dota and LoL 5vs5 players dominate the competitive scene. Mentality is changing and following those 2 games (and their other equivalent), people are most likely to be interested in teamgame and teamplay than only 1vs1. Same if teamplay means random team vs random team.
2- In the past, 1vs1 "appealing" was also most likely due to poor connectivity and computer capabilities. Running a 4vs4 SC or Coh1 wasn't something everybody could do 4-5 years ago. Today, apart from a bad configured 3dengine, nothing stop the majority of players playing 4vs4.
3- You are losing nothing, someone good in 1vs1 have greater chance to be good also in 4vs4. Micro and macro are dealt at another level. of course there are exception but those doesn't make the rule.
4- SC2 brought some good new concept with the base/resource sharing between team mates. Coh2 is still late and doesn't innovate enough in my opinion. Example, Attrition mod is really interesting but because it still an "unofficial" mod, it is not enough promoted and so cannot be improve and so bring more innovation and etc...
-5 Social aspect, team vs team bring more drama, more social, more interest to the community, so community has more interest and so can grow bigger.
Like I said, I think by the fact Relic isn't innovating in the game mode available and unable to improve the 4vs4 experience, they are restraining their own community in it potential expansion. People are bored of only watching competitive 1vs1 (same if it is always good to watch), they want to feel the other aspects of the game with large move, team play, simultaneous micro and macro etc...