Perhaps part of the reason for this is that the promises we read in the Bible don't say what we think they say. That is what H. Lynn Gardner argues in part one of his article When Our Prayer Requests Are Not Granted. Gardner writes:
People often speak of unanswered prayer. Is this the best term to use? It may wrongly suggest that God is either unable or unwilling to respond to our prayers when he may well answer in ways we do not recognize. Therefore, I prefer to speak of ungranted prayer requests.Gardner goes on to examine several of the Biblical promises concerning prayer and helps us understand their context. We need to remember this when we get frustrated with our prayers. I encourage you to read When Our Prayer Requests Are Not Granted.
Whenever we study the words of Scripture, we need to be careful not to take them out of their context. This is particularly true of Jesus’ prayer promises. Context controls meaning. Each promise should be read in the light of the statements surrounding it. To whom was the promise given? Does the context limit or qualify the meaning? What does the rest of Scripture teach?