If you look through the biblical record, God did at times speak through dreams to both believers (e.g. Daniel) and unbelievers (e.g. Abimelech, Nebuchadnezzar). However, you will note that these instances were few, and they always included a specific message that was just as accurate as direct fulfilled prophecy.
God no longer gives direct prophecy now that we have His entire Word. People who claim to receive direct messages from God are often simply faking it. It was never the biblical pattern for God to reveal new truth in dreams. It was rare in biblical times and would be even rarer today if God so chooses.