1) It's a great deal, even if you ignore Origin and redeem the Steam keys
It's hard to beat that price for one of the games, let alone the whole set. The deal just gets better if you redeem everything.
2) The charity bit
This builds goodwill with players, and nobody needs more goodwill than EA. The good deal was part of it, and the charity half makes them seem benevolent.
3) Many of the games offered have Origin-exclusive sequels either on Origin or coming this fall
It's a pretty ingenious way to hook users into the Origin platform. Give them a taste, then make them use Origin for the next game. Pretty simple.