Well if they stop working they make 0. 10% of any income is still more than zero, and this would likely be bracketed so high that there'd be at least a million or two in lower tax bands.

Edit: also strictly, the comment you replied to said "the wealthy" this could refer to a wealth tax rather than an income tax, where stopping working would just remove the income but not affect the tax burden at all—i.e. a pretty terrible idea if you want to remain wealthy