In 2015 or so, I was really surprised to hear that the Australian Stock Exchange was going full-steam ahead with a blockchain-based settlement platform. From memory, they were targeting 2020 or so for a full rollout.

Just checked and this has now been pushed back to 2023.

I know that there's been a lot of improvement since then, but once you reach a certain size, things just move very slowly. It's less about the tech, and more about the pace at which stakeholders get on board.