The costs of maintaining/operating chip-and-pin cards are higher than chip-and-signature cards. Also, chip-and-signature cards require a robust telecommunication network which US has and Europe doesn't. Long back in 1990s, when Europe first adopted EMV (chip-and-PIN), they didn't spend in their telecommunications network because it is much more expensive than it is in US. That's the reason they stuck to chip-and-PIN. US, on the other hand has an established telecommunication network.