Obviously Fischer was doing a little score settling here too. Botvinnik had always treated Fischer with contempt, as a devoted Stalinist, Botvinnik hated Fischer. So leaving Botvinnik off was pretty deliberate. On the other hand, He and Reshevsky cordially loathed each other (At the Buenos Aires tournament in 1964, Reshevsky told Taimanov, "I would settle for 19th place--if Fischer placed 20th.") but Bobbye certainly showed plenty of respect for Sammy's toughness.
In some sense, this wasnt so much a formal "10 Best" list, and more a list of Fischer's personal preferences. For instance, this interesting comment about Alekhine: "Alekhine has never been a hero of mine. I've never cared for his style of play: there's nothing light or breezy about it."
Hübner once showed that Fischer was right about Alekhine. In his books Alekhine used his analysis instead of the played moves to make his games shine brighter! Hübner could show this because he found differences between Alekhine's games in his books and other sources (like chess papers, tournament bulletins or game notes of Alekhine's opponents)! (By the way Lothar Schmid has one of the largest private chess libraries.)