Druke, my man :/
This is going to be kind of long, so buckle up.
Replaying act 1 makes me really want a prequel, especially since the devs have been rerunning some of the Rody and Druke events. I'm at chapter 3 in my replay of act one, and I just finished the scene with the Druke xahe-oyai and Norza. After the Blademaster Druke event a couple of weeks ago, I've been thinking about what Druke's motives for taking the aeon thorns were. Like, obviously he wanted to stay/become stronger despite his age (I don't think he's even that old? I assume he was somewhere in his 20s during the last Pandemonium, so he would have only been in his early forties or late thirties, which isn't that old.), but I feel like that deviates a bit from how his character was portrayed in the last two events (Blademaster and Witch of Winter).
When we first meet Druke in the Blademaster event, he's arrogant and eager to rush into battles if it means he can prove his strength. He's even glad that the Pandemonium has started because he's always wanted to fight in it. Druke and Norza (post-Menue's death) are pretty similar because they're always searching for that next big fight. Once Druke meets Rody and Rody is revealed to be the Crimson Crestbearer, Druke realizes that maybe there's more to fight for than just proving your strength. He swears to help/protect the Crimson Crestbearer and the act ends. Enter the Witch of Winter event. Druke is still his arrogant self, but it's less about growing his strength and more about helping Rody end the Pandemonium.
Now, how does this relate to act 1 chapter 3? The Witch of Winter event is only a short amount of time after the Blademaster event, but Druke has obviously found something new to fight for. If Druke's character motives have changed this much in the short time he's been traveling with Rody, imagine how much more he would have changed in the months (or maybe years?) leading up to Rody's battle with the Eternal. Maybe he even gave up entirely on seeking the next strongest enemy?
But, we know how Rody's battle with the Eternal ended. Rody and Druke were pretty good friends, so Rody's death probably hit him hard. Sure, their other traveling companions were still alive, but Rody was someone that Druke admired, which made their relationship kind of special. For some people (I think I can safely say that Norza and Druke fit into this category), losing the person that you admired can cause you to start sliding back into some bad habits. Once Druke lost the person he admired and wanted to protect, he probably started looking for something that would give his life meaning: becoming the strongest swordsman on Erden. Once he started getting older, he began losing confidence in his skills, and, despite having seen the outcomethanks to Xandra, he accepted the aeon thorns that Norza offered him.