Naive finance question: why do stocks have a an exchange they are listed on if they can trade on multiple exchanges and dark pools?

Productising RWAfi @plumenetwork. Building https://transferagentprotocol.xyz on it. Hosting /rwa and /plume and /nest

I feel like @thatalexpalmer.eth would know this

The only problem is externality pricing.

Building https://negationgame.com

Thanks @nor 

@dwr.eth dark pools fall under categories of brokerages (one who makes trades on your behalf) and ATS (alternative trading system).

Once a stock is allowed to trade on a national securities exchange, it's allowed to trade everywhere that abides by the same regulation.

A stock that trades on national securities exchange updates its price. Dark pools don't, because their purpose is semi-private trading.

Simplifying -> if Berkshire Hathaway wants to buy $9B worth of Apple stock, using an exchange would affect APPL price. By the time all $9B was bought, its price would be higher.

The main role is not centralization, it is reconciliation of records in disparate systems and having them all say the same thing.

Coordination of recorded data at scale is challenging, especially when that data is meant to be immutable.

Dark pools would make a global price index impossible.

right but the question is basically the opposite of this. Why not put everything into a dark pool?

Maybe a more ideological way to ask this question is: if the main role of an exchange is information centralization, then in a world where the goal is (sufficient) decentralization are there alternatives to the exchange?