It looks like they deliberately broke backward compatibility with existing infrastructure around 500-yen coins, perhaps so that they can better prevent the Korean 500-won hack.
Any machine that can handle the new 500-yen coin has probably been calibrated with lower tolerances to accept each version of the Japanese coin, but not the similarly-sized Korean coin with 1/10 the value. You can't just patch machines to accept a range of weights, because that would defeat one of the main purposes of introducing the new coin.
Meanwhile, you can still use the Korean 100-won coin to unlock any U.S. or Canadian shopping cart that takes a quarter. I don't know why South Korea ended up with coin sizes that are almost exactly the same as heavily-used coins in two of their closest economic partners, but they're probably stuck in the same situation as the Japanese: if they change their coins, they'll need to update a lot of existing machines.
> I don't know why South Korea ended up with coin sizes that are almost exactly the same as heavily-used coins in two of their closest economic partners
Easy to find coin mechanisms, and it increases the value of their currency, since the coins are useful outside the economy. ;)
Any machine that can handle the new 500-yen coin has probably been calibrated with lower tolerances to accept each version of the Japanese coin, but not the similarly-sized Korean coin with 1/10 the value. You can't just patch machines to accept a range of weights, because that would defeat one of the main purposes of introducing the new coin.
Meanwhile, you can still use the Korean 100-won coin to unlock any U.S. or Canadian shopping cart that takes a quarter. I don't know why South Korea ended up with coin sizes that are almost exactly the same as heavily-used coins in two of their closest economic partners, but they're probably stuck in the same situation as the Japanese: if they change their coins, they'll need to update a lot of existing machines.