Chinese 8 ball offers a level of difficulty between Snooker and American pool. Sinking balls is actually more difficult than Snooker but The strategy and positioning less so. Chinese tables have Snooker pockets and ‘nap’ snooker cloth.
Chinese 8 ball is the most popular game of billiards in the world so the question could be reversed...why do American tables have diamonds when most tables in billiards sports don’t?