Another INTJ here (early retired for 15 years). It's no surprise to me that a lot of FIRE enthusiasts are INTJ. If you're into FIRE then you're a planner who is happy with delayed gratification. That's INTJ to a tee.
Back in the early 2000s on the Berkshire Hathaway board on the American Motley Fool, there was quite a bit of discussion of Myers-Briggs types and investing. More than 50% of the posters were INTJ, with INTP coming second. Berkshire Hathaway, with its philosophy of no dividends and not prioritising short-term gains over long-term growth, clearly attracts INTJs.
FIRE requires people to prioritise saving over current consumption. One of the more interesting bits of scientific research on this topic is the Stanford Marshmallow test. Children were offered a treat (usually a marshmallow) which was placed in front of then, but they could instead have two treats if they waited roughly 15 minutes. Roughly one-third of the children ate the the treat immediately, one-third ate the treat after some delay whilst the remaining third waited for the two treats.
The follow up studies over the years showed that those didn't wait tended to be spendthrifts with poor impulse control whilst those who waited tended to be more successful and less reckless (and I suspect are much more likely to be FIRE candidates).
https://en.m.wikipedia.org/wiki/Stanfor ... experiment