Because truth, inevitably, demands change. And, let's face it, people hate change.

However, something else that I've observed which I think is more subtle, but equally as dangerous and destructive is that this same mentality of "the inconvenience of truth" is brought to our Christian walk - even after becoming a Christian. 

Let me explain.

As you start on your journey of knowing God and honouring Him, you will be confronted inevitably with depictions of God's wrath, God's Trinitarian nature, Hell, Jesus' manhood and godhood and many, many other perplexing and confounding concepts found in the Bible. These things are all a bit overwhelming and seem inconsistent to what you understand of God, especially if what was evangelized to you were centered on (or maybe even exclusively on) God's love and mercy and grace. 

So then you're confronted with a dilemma. How can both God's wrath and all those other things be co-existent when it seems like the existence of one negates the other? Thus, I think as a means to rationalize and reconcile the paradoxes that now are in your mind about God's character, you have to choose between which one you think is true, or maybe "more true". Because it is harder to see how they could both be true. 

However, when you do that, it is very tempting to choose the one that is more pleasant or more understandable to you. This is where I believe the whole "inconvenience of truth" problem comes in. It is way easier to believe in God's love, mercy and grace than to be confronted with the inconveniences of the truth of God's hatred for sin, His righteousness, and His judgement - all reliant upon His absolute holiness.  

In light of this, I honestly think that we often neglect what we do not want to confront to be true and we don't wrestle as much with these difficult concepts. We much favor an understanding of God simply limited to what we want to see and believe.

This is what I believe has led many Christians to honestly believe that there is no Hell. Or that if there was one, God wouldn't send people there. Or the notion of being "once saved, always saved", or the notion that God is not Trinitarian, or that Jesus couldn't be fully God and fully man while he was on Earth....etc.

Now, I don't want to bash these people, God knows that I am obviously not infallible myself. But I do think that if we are to say that we know God, then we have the obligation to really know his whole character and really wrestle with things that are beyond our understanding - especially when it seems like there is an inconvenient truth. And one of the most effective ways to do that that I've found is just to read your Bible honestly. To read it with the one notion of wanting to know more about God. You will discover very quickly that you will be confronted-very blatantly- with things that are contrary to what you thought was true. And when that happens, instead of dismissing the truth due to its inconvenience, to instead wrestle with it, and come to a bigger and better understanding of God. 

It is a continuous process but something that I've found to always ends in progress.