I think ISINs being used in Europe might even predate the EU taking charge of a lot of financial market regulation.
Probably they became more popular/important specifically because tickers did not, which in turn is probably because there are so many countries/exchanges that a global exchange-driven namespace was never really feasible?
Well, listings had domestic regulator control for the most part but I think you hit it on the head. Brokers in Amsterdam, London, Frankfurt, or Milan needed to access 15-20 countries worth of exchanges, and the curse in the EU is the multi-currency cross listings.
Easier, if somewhat more verbose, to use the three in combo to identify. Helped somewhat by the message volumes being a small fraction of what they are in the US. Less need to optimize on a per order, or per market data packet basis.
Also explains why FIX is more prevalent in EU markets than it is in the US.
Probably they became more popular/important specifically because tickers did not, which in turn is probably because there are so many countries/exchanges that a global exchange-driven namespace was never really feasible?