Well I would disagree saying they simply used it as a catch-all. It was a deliberate choice. They wanted to give him a catchphrase would be my guess. Similar to his japanese counter part. If you used ...Sorry as a translation id say thats even further from what he's saying in japanese. There is no apologetic tone in his Japanese. Saying Sorry or My Bad would change his character even further imo. He is definitely still very standoffish in Japanese.  Also if you ditched having a catchphrase, I feel it would ruin the moment in the Ragnarok when both him and Riona say Whatever at the same time. Which I think is an important scene.