1--only 35 films could be mentioned;
2--certain films perceived as marginally noir were bypassed by most voters.
Of the six films you list, only one (THEY WON'T BELIEVE ME) has been shown at NC SF. (ALL THE KING'S MEN was shown in Palm Springs this past May, possibly as a passive-aggressive reply to my calling out the FNF for not showing noirs with social justice themes, but certainly because it is a very fine film; just how noir it is we will look at in a moment.)
Here are the films quality rankings:
All The King's Men 90
A Face in the Crowd 91*
On The Waterfront 93*
They Won't Believe Me 88
Detective Story 85
*Adjusted down 2-3 points due to a "Kazan effect" in the "wisdom of the commons" data (more on this in a minute)
If all voters agree that these films are noir (more coming on this...), then you have four films that are certainly contenders for a Top 100 (depending on how you restructure the voting to accommodate more films).
But I think that three of these films--the first three on the list--are truly marginal in terms of film noir. As Mike Kuhns noted, his vote for ON THE WATERFRONT was knowingly against the grain of prevailing thought in 2005, which was that it's first and foremost a social drama dominated by Method acting. No one else voted for it despite its reputation, which indicates that most simply don't see it as a noir.
All three of these films score in the 90s on the Noir-o-Meter, again putting them all in a figurative "grey area" WRT noir. Given that, I think it's understandable (and not particularly surprising) that these three films received so little attention in the poll.
NOTORIOUS we know about--it's the Hitchcock conundrum. It was certainly in place in 2005, and might still exist at a fairly similar level today. One other factor, probably much less influential, was that the early versions of the Noir-o-Meter, which were presented, discussed and critiqued on the BB in 2004-5, had lower scores for films that prove to have more "melodrama" elements (several of which were inserted into the method after the Top 25 poll was taken). When the scores switched around a bit as a result, a number of Hitchcock films that had been in the 90s range on the Noir-o-Meter had their scores increase significantly; one of these was NOTORIOUS. So a few folks who voted may have had a subliminal impression from reading those earlier posts about "Hitchcock and noir" that NOTORIOUS was not really a noir.
As for THEY WON'T BELIEVE ME and DETECTIVE STORY, I would guess that the constricted ballot is the primary culprit. It was also still rather difficult to see certain noirs in 2005, and while I think DETECTIVE STORY was pretty well known due to its director (William Wyler) and its primary star (Kirk Douglas), the same could not be said for THEY WON'T BELIEVE ME (Irving Pichel and Robert Young). It almost certainly hadn't been seen by everyone.
(BTW, that lone "honorable mention" vote for THEY WON'T BELIEVE ME was from yours truly.)
I think DETECTIVE STORY might also have been bypassed because folks were rationing votes in order to spread them around, and supporting another clench-jawed Kirk Douglas performance beyond ACE IN THE HOLE was just not going to gain a lot of traction given the size of the ballot. (And many folks used their "honorable mention" votes to showcase personal favorites.) The other reason you covered: it's not really that good. In fact, there might be a bit of a "Wyler effect" that insinuated itself into a segment of criticism which got picked up by Maltin (who despite his omnivorous interests is exceptionally mainstream).
What year are we using for the Maltin grades? If it's relatively recent, it might be interesting to obtain one of the earliest editions (mid-to-late 80s)
Finally, the "Kazan effect," so called because films from the more distant past with a ton of votes tend to rise in the ratings. They tend to seriously outperform the "Top 1000 voters" in the IMDB polling results. That's clearly the case for ON THE WATERFRONT and also true to a lesser extent for FACE IN THE CROWD. And this affects those who post reviews and leave a grade as part of their post. So some additional adjustment is needed in such cases (films with upwards of 10,000 votes cast--and I usually check it for those with >5000 as well).