Slots are probably the biggest attraction in regular gambling, I don't know what is the most played on online gambling world or even what is the most gambled in crypto gambling world (maybe dice?) but in the real brick and mortar type of regular casinos, people gamble on slots the most, and by a big difference. The reason is you can literally put 100 dollars into a machine and play there for 10 hours and still get out with over 50 dollars while also getting free drinks and even maybe meals since you are gambling there (for most casinos).