Summed up in two words: Power corrupts.  The Roman Catholic church had left a lot of the great truths of early Christianity and became so focused on some of the earthly power and glory that they forgot or bypassed many of the teachings of Jesus and it got very corrupt.  One of the first and most obvious reasons (Luther had 95 to begin with), was the use of indulgences being used to build St. Peters in Rome.  This was a huge church and they needed a lot of funds to build it.  Next, this was indirectly related to the belief in purgatory.  Though Catholics point to one verse in the Apocrapha, there is little scriptural evidence to support this and this is another reason the church was needing reform.  Next, the church was conducted entirely in latin and not the vernacular of the common people.  So not only did this take a lot of the accountability of the church, many people really did not know about the true message of the Gospel.  Another part of this is the Bible was not in the hands of the ordinary so not everyone could read it.  There was the belief in the RC church that a true Catholic needed both grace and works to get to heaven and not grace and faith alone which was a cry of the reformers.  Along with this idea was the protestant call of sola scriptura where the RC church said scripture along with tradition.  There was the RC belief that after first grace, all other graces must be earned and it was not emphasized.  One of the results of this belief as well is people never knew if they were saved or not.  Part of this was that they believed one could lose their salvation as well so they were never secure in Christ.  In addition, they believed that the Pope had excessive power and many popes did not earn the office on spiritual merit but bought it or got it for being in a certain crowd and influencing a great deal of political power.  Also, the role of icons and saints played such a large part of a RC’s role in church that many reformers thought this needed to be scaled back.  In summary, there was a great number of reasons the RC needed reform in the early church because the Gospel had become corrupted and it was not very evident to the common person.