What people hand over freely is the receipt for a decision they already made about whose work it is.
Resources move when meaning moves. Once a work registers as something a person is building rather than something being built nearby, gold stops reading as security and starts reading as material, and the emotion attached to handing it over is eagerness instead of loss.
Yahweh asked for a willing spirit rather than a fixed share, which is why the tent got built by people who were changed by paying for it. A levy would have produced the same structure and a crowd that still has to be told what to do next, every time, forever.