I don't believe God is broadcasting an automatic message at us 24 hours a day!
I've found that He speaks when there is something to say, and that our attitude is the biggest factor in our ability/inability to hear Him. Many saints have told how they have sought God, but He will not answer. That "the heavens are as brass" when they pray. Or talk about the "dark night of the soul" when the close relationship with God they came to depend on seems to just disappear, and God goes completely silent on them for a long time. But these are just temporary conditions, trials if you will.
Most do not hear God's voice because they do not listen. First it requires faith, and they believe either that He doesn't exist or that He isn't interested in talking to humans anymore. Second it requires an obedient heart, one that is willing to do what is asked. Or maybe as a bare minimum, one that is willing to listen to God's requests; knowing full well that knowledge makes us accountable for our actions!
I find that God speaks mostly in the still small voice. That He will take a passage of scripture or the words spoken by another believer, and "inspire" them to mean a specific thing that applies directly to me. It is then my job to listen, and to weigh out the probability as to whether it was indeed God directing my thoughts, or simply coincidence.
There are rarely ever situations where I know it is God beyond all reasonable doubt. Generally I must deal with percentages, where if I find that I honestly feel the chances that it is indeed God leading me are greater that 50%, then I pursue that path.
I think God's purpose for leading any of us has little to do with anything we might actually accomplish, but everything to do with our hearts' attitude. Those who demand "proof" from Him before they act, will not get it. But to someone who really truly wishes to follow the Master, we can easily learn to lay our lives down and simply follow whatever He says, without feeling the need to be in control over who He is, or what He says.