I wondered the same thing when reading that article! From what I gathered, though, a lot of the reason why it's not more popularity has to do with the fact that

I wondered the same thing when reading that article! From what I gathered, though, a lot of the reason why it's not more popularity has to do with the fact that you need to actually defending your claims to the IRS or in court: Operating largely out of public view — in tax court, through arcane legislative provisions and in private negotiations with the Internal Revenue Service — the wealthy have used their influence to steadily whittle away at the government’s ability to tax them. The effect has been to create a kind of private tax system, catering to only several thousand Americans. That doesn't sound like the sort of easily scalable thing that makes sense to folks who might save a few grand a year. In fact, it sounds very expensive.