Opponents disappearing - Challenge has finished (?)

[Bretwalda76]

Today 2 of my 3 multiplayer games ended without any notice or discussion.

Operation Barbarossa 1941 with nihilimus playing Axis after the 10th turn and

Europe 1939 Small Fleet with Underseawagon playing also Axis after the 3rd (!) turn

Why? Isn't it customary to concede or drop a message if someone does not want to continue for any reason?

(If there was a technical difficulty I appologise)

[topolm]

Of course, normal players tend to communicate and discuss all contentious issues.
And those who suddenly stop playing for no reason are goats.