Only a handful of places with caves? There's limestone and caves (yes even flooded) in far more places than there are cave diving instructors or courses, although there are caves suitable for what you're calling cave diving on every continent except Antarctica.
Most of the lessons taught in the other areas (like the Canadian Rockies, or TN/AL/GA (tag), or Poland, or Iran) are to cavers who are already used to crawling through slightly thicker "water" (aka mud) so it's not a huge leap to do short crawl-like dives in terrible water with homemade equipment.