Why can't the developers do both - holidays _and_ core content?
They certainly could. However, assuming they do not have an infinite amount of employees, they'd have to take people away from one project to work on the holiday event. Are you willing to delay the first real "quest update" two weeks to put in Valentione's Day content? Are you willing to wait an extra two weeks for an AH? Two more weeks for job adjustments?
While we do not know that they aren't sitting on their bums right now, if they did release a big holiday event then we would know that they halted work on other projects to develop the holiday content. Assuming they did decide to half-*** the holiday stuff in order to focus on real concerns, they made the right choice.
Edited, Jan 25th 2011 3:40pm by Hydragyrum