The US always had the same currency, so shares are almost by design fungible between markets. Also the rise of Nasdaq made for a quick transition to broker-dealer (market maker driven) markets, which combined with fungible shares and NBBO lead to a centralisation of exchanges early on.
On the contrary, Europe had historically one market of primary listing per country/currency, and it took a long time to see the emergence of MTFs centralizing books in a single place. Don't be fooled though, the vast majority of European liquidity is now on CBOE (the leading MTF) and LSE (the leading primary market).
The US always had the same currency, so shares are almost by design fungible between markets. Also the rise of Nasdaq made for a quick transition to broker-dealer (market maker driven) markets, which combined with fungible shares and NBBO lead to a centralisation of exchanges early on.
On the contrary, Europe had historically one market of primary listing per country/currency, and it took a long time to see the emergence of MTFs centralizing books in a single place. Don't be fooled though, the vast majority of European liquidity is now on CBOE (the leading MTF) and LSE (the leading primary market).