Some miners and traders are also a gamblers and 30% is pure guessing, there is no way for us to calculate how much percents of all crypto wealth is in gambling. There is many sites, and probably every site have some high rollers, plus so many little players. Its already mentioned, but some fiat casinos now accept bitcoins, and how to track all that, almost impossible. Even thou 30% is guessing, I must admit that its reasonable assumption, maybe a bit high who knows, 30% out of 70 billion, market value of cryptocurrencies, is almost 21 billion, do you really think that people have so much money in bitcoin gambling? When you put things like this in dollars for me 30% maybe even sounds to high. I tried to find more informations about about this topic but I couldn`t, I doubt that we will hear right answer on this question.