Why did Paul not encourage marriage?
Paul did not encourage marriage because his converts faced persecution, and it is much easier to die for your faith if you are single than if you have a loved one to worry about. That was his only reason given in the context.
Les explains that Paul's converts, coming out of paganism in places like Galatia, Philippi, Thessalonica, Berea, Athens, Corinth, and Rome, immediately came under the pressure of persecution. Because it is so much easier to die for your faith if you are single than if you have a loved one to worry about, Paul did not really encourage marriage. Les says that was his only reason. The same context notes these believers had been steeped in pagan darkness, serving gods that were not gods at all but only wood or stone.