I think your basic reasoning may be correct, but it would seem that the trend of posts by "the same very few people" has been the opposite of what you describe, rather a constant negativity instead of the "golly gee the Ravens are neat" postings. For the past year or two there has been a core of folks that ridicule and bash anyone that dares to show optimism for a struggling player or unit, often labeling such posters as "homers", as if that should be a terrible thing.
So if your looking for a reason for decreased traffic, IMO the ones that have left, stopped posting or just don't join are turned of by the negativity and pessimism, not the lack of respectful and intelligent conversation of opinions, good or bad.