Well, there is a reason for all of this. A good place to start is right here ----->
www.newadvent.org/cathen/11604a.htm
Pelagianism taught that salvation could be achieved solely upright moral behavior which was possible for every human being, even without grace. This heresy called into question the sacraments, the Incarnation, and the doctrinal teachings of the Church.
Since, according to Pelagius, there is no original sin in the sense of an inherited sin from Adam and Eve’s original disobedience from God, Baptism washes away personal sins, not original sin. Salvation is achieved through an upstanding moral life, which every human being can lead by using his or her mind and free will. Baptism is not necessary for salvation. Clearly, this position calls into question the practice of infant Baptism
The fundamental problem with the Pelagian view of Christianity is that without original sin and its effects, we do not need a Redeemer. Christ and the Cross become unnecessary. Even Christ’s mission of Revelation is called into question because if our mind and will are not weakened by the effects of sin, we can know what we need to know - the moral law - without the necessity of Revelation.
Further, since the moral law is all we need to know, the mysteries of faith revealed by Christ which we cannot know through human reason, such as the Trinity, are unnecessary. Therefore, Christ is unnecessary. If Christ is unnecessary, then the Church is unnecessary.
Pelagius did not establish a rival Church organization to the Catholic Church. Partly, this lack of organization among Pelagians is attributable to the implications of Pelagianism: the Church was not necessary.
Taking a look at the history of Pelagianism, we can see how different aspects of his heresy, to a greater or lesser degree, have been embraced by the many offshoots of the Reformation whether they know it or not.