User blog comment:Rodrigo X/The Sims 2: Ultimate Collection for FREE at Origin (no need for base game!)/@comment-5520812-20140723192036/@comment-1809104-20140723204230

When they said it was available only to the ones with The Sims 2 at Origin, they quickly announced that today (23/07/2014) there would be instructions for non-Origin players. At first it seemed people would need to supply their product codes (since you can't register DVD games on Origin, tried it myself), but EA probably thought that would be an unnecesary hassle and decided to release it completely for free.

As for their intentions, I'm guessing this is a simple but effective way of attracting people to Origin. And I can see why; I'm almost always online at Steam but rarely on Origin (usually to just start Burnout Paradise, which I got for free on it).