The bible gives us several reasons, but according to Jeremy Taylor, a deceitful heart is at the root of prayerlessness.
Why Can't I Pray?
August 18, 2012
The heart is deceitful above all things and beyond cure. Who can understand it? Jeremiah 17:9
Jeremy Taylor (1613-1667) preached a sermon titled THE DECEITFULNESS OF THE HEART. And one key proof of its existence can be found in the ongoing struggle that is the human experience to pray.
We put on strange fire, and put out the fire upon our hearths by letting in a glaring sun-beam, the fire of lust, or the heats of an angry spirit, to quench the fires of God, and suppress the sweet could of incense.
The heart of man does not have strength enough to think one good thought of itself; it cannot command its own attention to a prayer of ten lines long, but before its end wanders after something that is to no purpose; and no wonder than that it grow weary of a holy religion, which consists of so many part as make the business of a whole life.
And there is no greater argument in the world of our spiritual weakness, and falseness of our hearts in the matters of religion, than the backwardness which most men have always, and all men have sometimes, to say their prayers; so weary of their length, so glad when they are done, so witty to excuse and frustrate an opportunity: and yet there we do not trouble ourselves in the duty, or weary ourselves, or labor violently.
We do not beg a blessing and rarely rejoice in receiving it. There is not the sense of having the greatest honor of speaking to the greatest person and greatest King of the world.
And that we should be unwilling to do this! We are unable to continue in it, and we are so backward that we cannot return to it. Where is the gust and relish in doing it? We are unable to comprehend the value of the nature of the thing within us. We have a strange sickness of the heart, a spiritual nauseating of loathing of Manna, something that has no name. What else could explain all this but a weak, a faint, and false heart?
Yet you have not called upon me, O Jacob, you have not wearied yourselves for me, O Israel. Isaiah 43:22