Not sure where you got the thing about the cost, which doesn't seem to be in the article, but it also flatly states that "The people who flee tend to be ultra-wealthy, and many of them are seeking to reduce their tax burden."
The article talks about the ultra wealthy, but they have the power, money and means to easily deal with the citizenship taxation bs. I don't care about them.
The problem is that those rules are punishing regular people.
I know one person who wasn't allowed to open bank accounts because of her citizenship. Another who yearly gets stressad out because filing US taxes is such a grueling process compared to the local process where you're done within ten minutes. Another wants to renounce citizenship because he doesn't want to deal with the bureaucracy, but he cannot afford it.
They all live in Sweden, which I doubt anyone sane would consider a tax haven.
If Eritrea is the only other country in the world that implements similar draconian tax laws, maybe there's something wrong with those laws?