Can anyone explain why Faster-RCNN has bbox regressors at two different stages?

– Region Proposal Network (RPN): anchor deltas

– Fast RCNN: bbox predictor

Aren’t they doing the same thing? What’s the idea behind having a bbox predictor at the final stage when RPN has already computed an anchor (which along with its delta can be treated as the bbox)?

I’m most likely missing something. Any clarification would be appreciated!

Thanks for reading!