To answer the question posted under "Why":
I think that there is a fine line between following God for the blessings and following God and accepting the blessings. If one were to simply chase the gain, they really wouldn't be following God to the fullest extent. "No one can serve two masters; for either he will hate the one and love the other, or he will be devoted to one and despise the other. You cannot serve God and wealth" (Matthew 6:24) One example of this is when Annanias and Sapphira were giving to the Church in Jeruselem and they withheld part of their earnings. (See Acts 5.) They seemingly were serving God, but the Holy Spirit wasn't fooled. In their hearts they were seeking gain from God and from men. (I'm not going to guess at the state of their souls at the time of their death, but the point is that they were not following God.)
A counter example to look at is that of Abram. In Genesis 12 God commanded him to leave his home and wander about. God promised blessings for doing so, and Abram went. Now whether his motive was the gain or God is not clear, but he was following God's command and God blessed Him for it like He promised.
All that to say: we should follow God's commands, and where blessings are promised we should expect and even look forward to them, but we should not make the rewards our ultimate goal. (I don't know about all my readers, but I can't wait for the reward I'll get at the end of this life.)
(Matthew 6:24, Acts 5:1-11, Genesis 12)