From the early 1920s till the early to mid 60s, the 4 major sports in America were, in no particular order, Baseball, College Football, Boxing, and Horse Racing.
Newspaper columnists were a huge influence on the way each was viewed. The big city papers in New York, Boston, Philadelphia, DC, Chicago, and St. Louis reported on, glamorized, and made heroes of the various stars of the day. People would gather around their radios if they couldn't go to the sporting event in person, and they would cheer on these heroes. So, it doesn't surprise that these players, some reaching mythical proportions, would be remembered so fondly. Even those of us that didn't see some of them play, can still talk about them as if we did.
The paradigm shift started happening with the advent of television, and the population shift westward. We didn't rely on the columnists to form our opinion. We watched our heroes on the screen. We could see their flaws along with their accomplishments. While the players overall, with each generation, are more athletic, better trained, even more skilled, we don't idolize them the way we used to.