StarForce 3 - Difficult or easy to crack???

[MontyBurns1985]

I am really wondering why some games which are StarForce3-protected are cracked very fast, some after a long time and some still have not been cracked, yet.

Games, which are StarForce 3 protected:

1. Codename: Panzers - Phase One (was cracked very fast!)
2. Codename: Panzers - Phase Two (has not been released yet, but will probably be StarForce3-protected!)
3. DTM Race Driver 2 (still not really cracked!)
4. GTR - FIA GT Racing Game (still not really cracked!)
5. Obscure (cracked, but took a long time!)
6. Singles - Flirt up your life! (was cracked very fast!)
7. Singles 2 - Wilde Zeiten (was cracked very fast!)
8. Splinter Cell 3 - Chaos Theory (still not cracked!)
9. Trackmania (was cracked very fast!)
10. Trackmania Sunrise (still not cracked!)

I really don't understand why for example "Singles 2" was cracked after some days, although it uses a very new version of StarForce 3 and for example "DTM Race Driver 2", which is much older and uses a much older version of StarForce 3 has still NOT been cracked.
Does anybody can tell me why?