Moving Eaglercraft from version 1.8.8 to 1.21 isn't as simple as clicking an "update" button. There are three main challenges:
A high-damage weapon that rewards players for falling from heights. Can Eaglercraft Actually Reach 1.21? eaglercraft 1.21
If an Eaglercraft 1.21 version were to release today, it would include some of the most transformative features in Minecraft history: Moving Eaglercraft from version 1