A Darn Good Question
Here's a good starting point for discussion thanks to Corey over at Learning to Listen:

A lady came to a pastor who had been emphasizing discipleship and said, "I just want to be a Christian. I don't want to be a disciple. I like my life the way it is. I believe that Jesus died for my sins, and I will be with him when I die. Why do I have to be a disciple?" (question courtesy of Dallas Willard)

No, I don't have an easy answer to this one. But I did think of one of the underlying reasons that so many of us may not want to take that extra step from accepting to following into discipleship.

We don't want to grow up. We don't want to move from being children or teenagers into adulthood.

This is as true in most of life as it is here. Becoming adult moves us into needing to take responsibility for our lives and loves and actions and successes and mistakes. Becoming adult takes away our excuses.

Perhaps there is also a fear involved in all of this. We think that if we end up becoming disciples, God will give us some awful, horrible, detestable job He wants us to do. Somehow or another we have come to equate being a "disciple" with a task we gotta do whether we like it or not.

But I don't think I have ever met a real disciple who felt that way. They truly enjoy being a disciple. They get joy and peace and excitement and hope out of everything they do for Jesus. Yet they are also not the obnoxious, self-righteous caricature that we may be afraid of becoming. They are genuine, honest, loving, caring people. Disciples may not even appear all that "religious" but everything they do is about Jesus. They may not talk about Him all the time, but they are always walking with him.

Now, of course, I'm going to have to go back to Dallas Willard's book and find out what he had to say. But in the end, if one believes that Jesus is who he claims to be; if Jesus is the one that Scriptures explain him to be; if Jesus did die for me as our Christian theology has proclaimed for 20 centuries, then I will soon discover the joy that comes from living for him and I won't be able to stop.

In short, I will become a mature, growing day-by-day, disciple.