I ran the Texas smash scene (melee) from 2004-2008. From 2008 to 2013 i switched over to brawl and i see a MASSIVE difference which i feel can explain why each game sells better than the last.
Melee game is by far the best (competitively) of all 3 games and the FIRST smash game to go "competitive." Any time a game goes competitive it sells more than it would had it been casual ONLY. But to be able to compete at a high level in melee, it takes TONS of tech skill as well as fast paced planning. Meaning, the learning curve is really steep. That was a major turn off to casuals/new players aka the largest base of potential buyers.
Brawl comes out and 4 things happened:
1. The wii install base was MUCH larger than the GCN base so that helps with sales.
2. Brawl is slower/less technical which allows causals/new players to pick up the game and compete much easier than they could with melee.
3. The brawl competitive scene reached high levels of advertisement/competition (evo/mlg...ect) much earlier in its life than melee did so it brought in people while the game was still fresh.
4. Brawl is the BIGGEST game of the 3. It has more content than ssb/ssbm combines. More stages/characters/items/modes. A huge campaign modes, online, stage builder and more. Whether those options are "good" or not is an opinion but u cannot deny that more content gave more players more things to do (which cannot be said for most fighters).
