yes, that is correct. If one is so sure about the price movements then should buy coins and make a profit. Because by chance if prices move in other direction in gambling you will lose all your funds but in trading, you lose only some % of investments.
Mian reason people go to these sites is they can get a chance to double or more within a short time so they are ready to take these big risks of losing their money.
Investing we need big amount, but to predicting and betting, we don't need more money. Just put some money on betting if their predictions are right they will get double profit in short time. So some people will bet on cryptocurrencies price. I think no one will predict 100% correct they just guess the future if it works they will get profit, or else they lose money that's it.