One big problem preventing the five factor model from catching on is that the five factor model seems to have value judgements built in (agreeableness friendly/compassionate vs. challenging/detached seems to imply that it is a good thing, so a lack of it would be bad), whereas MBTI makes both ends of the spectrum sound positive (in Thinking vs Feeling, Thinking sounds equally good, vs challenging/detached).
Another facet is that MBTI assumes bimodal distributions, but as a result they can come up with catchy characters like "The Debater" and "The Entertainer" which five-factor doesn't do.
As a result, people tend to talk MBTI, even among folks who know about the five factor model, just because it's easier. It has some amount of predictive power, much better than a horoscope or tarot cards or blood type or astrology, and the reality is that people talk about that stuff all the time.