Well, while I would always like more to the seasonal festivals, I wouldn't want to see them take work away from the normal patches to spend on doing seasonal events. At the end of the day seasonal events are just passing things that last a few weeks. Patch content usually has to last at least 3.5 months. The more elaborate the seasonal events are the more work and development resources that will be used on them instead of the normal patch drops.

The other limitation is seasonal events are inevitably held in ARR zones since they want them to be accessible to low level players.