A1. In that sentence "for you" relates to the "point". When the exercise is completed, somebody gets a point (achieves the goal). The goal is given to somebody (or the point is awarded) to achieve. When we talk of gifts (or awards), we use noun-preposition-noun phrases. "This gift is for you".
A2. You can't replace it with that sentence because it lacks the preposition that would connect the two nouns, and "you" cannot be "the point".
B. First off, that sentence is not entirely grammatically correct. It's colloquial. The correct sentence would end "...for his leaving".
B1. The verb "blame" is transitive. It can have a direct object and an indirect object. The accepted grammatical construct is "blame {direct obj} for {indirect obj}", for instance "blame somebody for something". The direct object is the target of the blame (accusation) and the indirect object is the reason for the blame. In this sentence "him leaving" is the indirect object of the verb blame (and "myself" is the direct object).
B2. Yes, and that would actually be much more proper.