Absolutely clear and honest would be something lie "we intend to take your free labor, declare it our property forever, make money of it en put it in our own pockets".

No one would consent to that, so organizations use weasel words or bury it in the small print. Mostly, they just obfuscate the consequences. Especially the "property" and "money" bits.

And yes, that is a "trick", even though by some definitions they are "clear" about it. Thousands of lawyers make a good living off that distinction.