The same happened on all servers / be it euro, german or whatever else. One lesson should be to give players a better feeling of control aka beside serverwide rewards, better personal rewards as well/ maybe quastbased and scaled to level, like finish x adventures or donate y items or combinations of goals that will help an overall server goal
Also good to have random extra rewards - maybe from the subquests - there are many options to get more people involved and make involvement somewhat more " in control" Events on a server basis are just too hard for people to feel able to control. If i see how much effort has been put in by some and how small a dent this made in percentages- it is no wonder people signed off on impossible goals. Achievable goals at individual level or guildlevel are much more influencable by people and hence will get more commitment