The 2 projects per game is a recommendation only, AFAIK. You can play with 4 projects online, for example. But for the physcial game it would be impractical/uneconomical to distribute 20 cubes per player, in case 6 players decided to do a game with all of them. So since there has to be a limit, it allows a bit more freedom to allow more Projects but limit the cubes, instead of making "max 2 projects per game" a hard rule.
Of course, this is all my interpretation only.