I've been wondering this myself. 8 seems very Fi-ish--screw what society says, do it your own way. Justice. War vs Peace.
When I start talking about how I experience my 8-fix, others have told me it really sounds "more Fi"--Justice. War vs Peace. Screw society. Lol.
It's possible that many 8s mistype as Thinkers, for one thing. I personally type strongly on Sensing/Thinking, and I'm 99% sure it's the 8-fix that influences that.
I am capable of being--
- blunt and insensitive
- more concerned with justice and fairness than interpersonal considerations
- outwardly cold and unfeeling
- value my ability to think logically and clearly (could be 5ish)
- see most emotional displays as "sentimental" and therefore "weak"
- avoid expressing feelings due to vulnerability/inherent aversion to doing so
- and I could probably list all the criteria of "Thinking"
It was really hard for me to accept I was more likely a "Feeler". I'm "obviously" a Thinker, lol.
So, that may be one reason there's a dearth of Feeling 8s--simple mistyping! I know that ExFP 8s do exist, and I've heard reports of INFJ 8s as well.