- so there's somebody in France that can *make money* being the middle man
- so the French broker can be held to some standards reporting and what not. For example, the French broker at risk of criminal prosecution cannot sell shares to NK or Iran.
- so the rules around transfer of shares for payment and settlement are set so people can't be screwing each over or not completing settlement in a timely fashion
- because of scale: there are zillions of trades done every day. that's why netting-out is a real thing. settlement has to be fast, tight, nailed down. And regulation helps with that through known pre-approved brokers with set roles and responsibilities
Also consider that unlike crypto you gotta settle. Settlement is serious. And settle in a bonafide currency that everybody agrees is a currency: EUR, for example. And you have fixed time to do it in.
You can't be waving your hands with some stupid story about how your broker/holder of crypto,
- stopped you from withdrawing your stuff
- is down
- is in chapter 7 or 11
- that you forgot your crypto keys
- and the entity getting the cash for selling shares isn't gonna wait around for some miner to "approve" your transfer maybe in 10 mins ... or maybe tomorrow