Why does Paul not praise the Corinthians in 1 Corinthians?
Paul does not praise them because this letter addresses their problems, not matters he can commend. He is too kind to condemn outright, but he neither commends nor brags about their behavior. They remained carnal and fleshly minded, more than any other church Paul dealt with, so he could not approve their conduct.
Les explains that the Holy Spirit inspired Paul to write 1 Corinthians, yet the letter also reflects the human element: it responds to questions the Corinthians had written to him. They had many problems and questions, and the whole letter deals with problems for which Paul does not commend them. Les teaches that Paul is too kind to condemn them outright, but neither does he commend them or brag on them. He backs into the situation so he does not flare their anger and put them where he cannot deal with them, while still not agreeing with their problems. The underlying reason is that they were still carnal; of all the churches Paul dealt with, none were as carnal and fleshly minded as Corinth. Reading the content makes this evident.