Here where I live in Spain, chains are often required when driving through certain mountainous areas in bad conditions.

Why are they not consistent a good option? Conversely, is there some reason why I never hear anything about snow tires here? I guess it's because snowy conditions would be a very occasional and short term situation for most drivers here (excepting those who live in the mountains, which is a very small proportion of those who drove through the mountains). Would snow tires be a viable replacement for chains or do they serve different purposes? Can you leave snow tires on all year round?