Why did the four groups in the Corinthian church grieve the apostle Paul so much?

Les explains that Paul wrote 2 Corinthians to the congregation at Corinth, which had been a carnal church that had not grown into the deeper things of Paul's teachings. In the first letter, Paul constantly upbraided and reproved them for their carnality, and one main problem was divisions in the church. Even in that small group there were four distinct divisions: some said they followed Christ and His teachings, another group followed Peter, a third followed Apollos, and a fourth said they had heard the gospel through Paul and would follow him. Les teaches that these four groups caused much dissension and grief to the apostle, and this was part and parcel of their carnality; they simply did not grow spiritually. Les also notes that gross immorality in chapter 5 grieved the apostle because a believer would stoop to such a low level and the church was not addressing it. By 2 Corinthians, many things evidently had been corrected, showing the first letter did not fall on deaf ears.