Well, aside from the population issue (or, perhaps, related to it), I've seen the claim (reasonably well substantiated in various ways, imo) that 4s and 5s are often the least healthy types on the enneagram (6s as well [but they, along with 9s, are one of the types least likely to actually know their true type]). This could explain why so many 4s and 5s visit internet forums and start threads to discuss their issues; because they are more in need of trying to work through this unhealth.
The Justice Fighter
XXXX - XwX Xdw XwX sx/so - Neutral Good
"I trust what you are doing though…I just see it a little differently.
I don’t see it as you stepping away from the fire. I see it as the fire directing your course.
No matter how airy or earthy or watery you become... to many of us you will always be...a super nova."
"Behind these gates of seeming warmth sits, loosely chained, a fierce attack dog. Perhaps not crazy, but dangerous"