As bulletproofs were really new, and the initial implementation made by the group, while thoroughly done, needed a rewrite focused on our specific use-case, implementing bulletproof in Monero was not a simple thing.
Bulletproofs also have the advantage to allow to prove that multiple committed amounts are in the desired range at once. No need to prove each output to each destination in separate proofs; the whole transaction amounts could be proven in one bigger (but still very small) bulletproof.
