I don't understand those that don't show and can show but just aren't in the mood or something at that time. Most of the time they need the certain event done too whether it be a mission, quest, end game, etc. so why not get it over and done with while it's already scheduled to happen?
I find it annoying too, but also noticed a lot of people haven't been on lately, I guess because of this login issue... :/ It's no wonder the last couple of weeks for Salvage gathering time has only been a few people, and normally my assault LS is filled with 10+ people at least at a given time during the nights it runs, but it's been less than that for a week or so.
Other than that, it's always good to hear from people if they can't show. This kinda thing used to piss me off the most though during my CoP statics when we had so many members in the past saying they'll come for the certain time and night, and then never even show up or anything. The funny thing too, coincidentally it always seemed to be elvaan tanks 90% of the time...