Why was John 8:1-11 removed from some Greek manuscripts?

“The episode of the woman, covering the first eleven verses, is not found in some of the better manuscripts. As I am sure you know, our English Bibles are translated from the original languages. The New Testament was first written in the Greek language. Extant manuscripts were used to compile a Greek New Testament; then our English translations were made from that. The Greek text of Westcott and Hort omits the incident of the woman taken in adultery from its position in the eight chapter of John but inserts it at the end of that gospel. Nestle’s Greek text includes it but encloses it in brackets. Augustine writes that it was omitted because of a prudish fear that it would encourage adultery. However, if you read the account carefully, we will see that it does not condone sin. Rather, it condemns sin. We have both a scholarly and moral basis for considering it part of the inspired Word of God.”

–J. Vernon McGee, Thru the Bible with J. Vernon McGee, Vol IV. Matthew through Romans, Nashville: Thomas Nelson, 1983, p. 414.