Mainly because we run from God.
At one level, we're comfortable in our delusions and we don't want to disavow ourselves of them. At another level, we carry with us shame and guilt. At a third level, we fear that God will reject us. And, quite frankly, we don't want to be accountable for becoming something more.
The best, and really the only, remedy for our inner barriers is to believe two things with all our heart and soul.
First, God didn't create, redeem, and/or sanctify us only to want to condemn us. In other words, He created us out of love, and extends to us every mercy. Not to mention, of course, that Christ walked in our very shoes and knows first hand the difficulties of being human. Thus, He wants to hear from us (for prayer is the divine language) and gather us to Him (for authenticity in prayer is a proof of your desire to be with Him in eternity).
Second, God knows you ("Even the hairs of your head are all counted," Matthew 10:30). He knew you before you were born, sees all of your struggles now, and wants to heal you of all your wounds.
So, reach out in earnest with your vocal prayers. Then, sit back and let Him invade your soul. This is contemplation. This is the prayer of the mind in the heart.