I am familiar with Octopus. Asian countries are different from the West because of the lower penetration of bank accounts and cards, due to lower incomes but also culture. Asia tends to be cash-heavy far beyond the West.
Japan in particular has western levels of banking and credit cards, but nobody actually uses electronic payments, hence relatively high use of stored value systems. Basically, electronic payments were forced upon them by transit, so it gets used for small-value transactions. This is part of the "Galápagos syndrome" of Japan, they do things differently due to culture so their systems are not necessarily exportable.
The opposite would be Singapore, which does have high penetration of contactless credit/debit for all kinds of transactions, and now has contactless transit. In Singapore, you use full EMV contactless where the Japanese use their IC cards.
Basically, the other poster doesn't understand that Japan has a problem: that Japanese refuse to use card payments even though their banking system is perfectly fine for this, and their invented solution: use of transit cards to stand in as a low-value debit card. And that problem doesn't apply to most Western countries who use cards just fine, and therefore there is no need to adopt a stored-value solution here.
