Why didn't Fischer consider him among the greats?
Fischer didn't think that a world champion should play in Lasker's style. Lasker played the man/opponent and Fischer believed you should play the board and not the man.... Lasker was known to make second rate moves in order to make the position as unpleasant as possible for his opponent and Fischer thought this beneath a WC and I believe this is why he thought less of Lasker.
That makes sense. However, wasn't it convincingly proven that the suggestion that Lasker played second rate moves was incorrect - perpetrated by the likes of Jankowski who were incapable of understanding his play.
I would have thought that Fischer would have seen through this.
The Kramnik interview is interesting and there is too much in it to comment on all of it, but some of the things he says about Lasker look a bit odd. The Lasker-Steinitz match exhibited a "huge gap" and Kramnik estimated it to have been a match between a 2700 and a 2400, yet the result was +10 - 5 = 4 for Lasker, not such a crushing victory. (Not mentioning that Steinitz was nearing 60 and his health and financial situation were deteriorating.) On the other hand, the Lasker-Capablanca match for him was the first WCH match in which both competitors played at a very strong level, yet Lasker didn't win even a single game in that match, and even resigned the match before it was officially over. Go figure.