I think CO is worried that too many people were seeing the new departure time and not arriving for their originally scheduled departure, then complaining when the time moved back up towards the original time. In other words, we can tell you that you're likelly to be late arriving, but you should still show up on time.

Can't say that I completely blame them. Despite the disclaimer that used to appear admonishing you to arrive at the sked departure time I know that they have had to deal with upset pax who were "told by CO" that the flight was late.