With everything that is going on, the one thing that brings people back is the player interaction. If a game can be played to its finish, the winner walks away feeling a true sense of accomplishment. More often than not, the game ends because some of the players just have to go home. In PBEM there are always 7 players eagerly awaiting a game start. So, you won't have to play with Italy in Civil Disorder at the start of the game.
Turns are usually every two weeks.
This gives you enough time to contact all the other players every turn. The part of the game that everyone likes, the diplomacy part, can be enjoyed to its fullest. The downside is that a short game will take close to 8 months to complete, with most games taking 12 months. PBEM are virtually the same game with one exception. Two turns every two weeks is not that much different than one every month.