These apps claim to let you turn your knowledge into money. What this means is the insiders get to cash out and the desperate suckers provide the liquidity. I'm amazed they've all gotten away with this for so long.
They've 'gotten away with' it by for example winning cases deciding they offer commodities trading, not gambling. (You can disagree with it, it's in the open and explicit is my point.)
They get away with it by having on the payroll the son of the president of the most powerful (and dangerous) country in the world