Forgot to Like your post. I´m agreeing with it, because its crucial to realise that even today, the number of real outstanding big men at boxing isn´t that high. The amount of tall and very successful SHWs of course depends on the pool size of existing tall men who get into boxing. Your post is absolute appropriate because the title of the threads makes the wrong assumption that its more depending on existing big men improving rather than the simple chance to find talented SHWs depending on pool size of bigger men itself. So yes, the correct answer is: They couldn´t improve because they didn´t exist. More tall men from the 70s onwards lead to a higher chance of finding some special fighters.
By the way, a much better question to adress the issue might be: "According to the normal distribution of height (mean = 5'8"), why didn´t the 6'2" - 6'3" HWs dominate the 50s?"
It's interesting that the champs of the 1950s (Charles, Walcott, Marciano, Patterson, Johansson) were not as tall as those in the 1930s (Schmeling, Sharkey, Carnera, Baer, Braddock, Louis) .
