scammers thrived more due to centralized exchanges being easier to hack:
See binance, mtgox, and every other exchange that was hacked.
Ok, so you are referring to the overal security of the system, an exchanged built on a blockchain platform to be more resistant to hacking, got ya! I think Binance has a decentralized exchange coding competition for the purpose of building one in the near future.
They want their finances to be handled by a 3rd party for a few reasons some which are critical due to multi-tasking.
This wasn't properly but nevermind it's irrelevant.