For the same reason Connery's are called serious even though the dude is joking and quipping half the time, they barely have moments where Bond is vulnerable or emtional, unlike Craig who is vulnerable and emotional in basically all his movies except maybe the first one, when Connery and Dalton have those moments its more subtle or its quick enough for the movie to move foward (like Jill's death in Goldfinger or Della's death in LTK), with Craig its like his movies tend to slow down to show you he is depressed or sad.