You a millionare yet?
I would write a book on Soviet hockey history right away, if I could find a publisher (sure I would
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As far as your question goes, I guess the reasons are:
it wasn't the best possible Team Canada and, like with NHL and Canada in '79 and '81, respectively, (WHA's Team) Canada lost the series. I'm not so sure, though, that the 1979 Challenge Cup gets much recognition nowadays either (IMO partly justifiably, partly not quite so). Also, it was only 2 years after THE Summit series, and maybe people just couldn't get into it nearly the same way as in '72.
I have to admit that I'm not so high on the '74 series either. I think that both Soviet hockey and Canadian hockey improved greatly from the '72 and '74 series. The hockey just wasn't as good or enjoyable as later on.
Then again, the '74 series had guys like Hull, Howe, Cheevers... Kharlamov, Tretiak, Maltsev, Mikhailov, Petrov... (not all in their primes or at their best) playing and the series had some unforgettable moments. For example, I don't think that even much better Canadian teams (on paper) ever played a better game than WHA's Team Canada did in the 2nd game of the series (if it wasn't for Tretiak's great play and Canada's less-than-great shooting, they would've scored something like 20 goals).
All in all, the '74 Summit series maybe deserves some more recognition, but how much? I don't know. Where would you place it?