If we step back we could look at this another way (as I do):
The following statements are simply me putting out the picnic table - I'm not being preachy here so don't worry!
1/ We are primarily spiritual (not physical).
2/ Our ability to communicate is far more based upon intuition and feeling that we normally realise - actual voices (either through the air or the imagination - like when reading this post) are the least effective form of communication we have.
3/ We can receive information much better through vision, smell, touch and sound than we can through language.
4/ Most of our relationships and communication is what I could term 'spiritual' - we can feel what someone wants the closer we are to them and the longer we have known them. My relationship with my wife is better now than it was at the beginning and we don't need to speak so often tog convey our feelings.
5/ Thus we come full circle - when we pray we receive a feeling, we are unable to hide or mangle our communication with language - when we pray often enough we feel how our lives should be, we become better people, we have new ideas - less selfish ideas - , we have inspiration, we begin to feel love / peace / a desire for purity and the good of our fellowman.
6/ Answers to prayer have rarely been verbal in my experience but have been absolutely life changing.
6/ Those who do not feel they have had answers to their prayers maybe were looking for the imperfection of voice and trusting less in the power of their thoughts and feelings.