Well, obviously they can't. This is especially so for American citizens who are citizen by blood, have never set foot in the US, and have no family to visit.

But notice how they've been working on new rules like FATCA that go after the citizen's bank, assuming the bank does any sort of business in the US?

For all I know, in 10 years the IRS will force the bank to extract penalties directly from someone's account.

the founder of a big french game studio filled for ipo two years after giving up his green card (not even citizenship).

the irs got the french gov to freeze all his assets claiming he was giving up citizenship to evade taxes.