[Within Silence]

Because these promises are not from God, but from the mind of those authors who spoke/wrote them, then they were put into a book called the bible and said it came from God. So basically the basis of your question is built upon a false foundation, which then negates the possibility for a solid answer. In other words, God did not say these words, because a true God would not be so ignorant so as to make false predictions, but rather, ignorant minds make false predictions/assumption/expectations/speculations which they say "are sent/told" by God which then do not come to fruition and then the people blame God for these false foundations/promises they themselves conjured up in their own minds and believed to be "the truth."

Proof is in the taste of the pudding, the reason these promises do not come true is for the simple fact that they are not true, which is validated by the fact that they do not come true. Its very very simple to see, not complex.