(1) Many people don't know that they're "US citizens" (2) Even if you are aware of (1) you have to know of this unique bit of US taxation BS, and know that tha

(1) Many people don't know that they're "US citizens" (2) Even if you are aware of (1) you have to know of this unique bit of US taxation BS, and know that that means you have to file a US tax return (something that functionally costs money) to not be breaking the law and so be subject to fines. (3) Even if you do realize that you need to renunciate your citizenship you have to do it in person, so you have to have the ability to also get to a US embassy, and hilariously prove you're a US citizen. (4) As the article states: renunciation itself also costs money, in addition to the other costs incurred. Given (1), many impacted people don't ever actually interact with the US government, and with (2) never occurs to them that they need to do anything. (3) and (4) then add an actual barrier to renunciation, couple with the potential "immigration" impact (Flying through LAX, NYC, etc can become questionable, which is a problem given they're major hubs), means that you actually get stuck in a damned if you do, damned if you don't. Finally, despite it being ostensibly a legal right, the US government has a track record of denying basic constitutionally guaranteed rights, and renunciation is no different. Because of (3) it's necessary to make an appointment and visit in person, and the US has actively ensured that that isn't possible by understaffing and even simply canceling appointments. So while only ~2700 may have renounced citizenship, the actual backlog is in the tens of thousands.