Some Christians never experience God speaking to them in personal, powerful ways.
Though they read their bibles, and read the book of Acts, their lack of experience of Gods voice, means they filter it and interpret the supernatural out of the Christian life. They are Christians, but they never experience the fullness of Gods revelation. This is not meant to be judgemental, it is an observation.

There may be different reasons, unbelief, no desire to hear more, God has His own reasons.....

I have heard from God in 'charisma' ways a few times, most often when I was under spiritual attack, at a crisis point, or deep in prayer and fasting.......

All of us say we want to hear from God, and sometimes we desperatly seek Him and don't hear from Him.
Its not an easy question to answer, why doesn't God speak to me.
But I do know what we can do to best place ourselves so God will speak.

Experience spiritual attack
Have a crisis time
Seek Him in prayer and fasting
Find yourself at a place and an opportunity where God needs to direct you.

Do you want God to speak to you, if He did would it change anything......or are you pretty content with how everything is?