This sounds like a major flaw in the logic of the study: "In MLB history, 64.5% of all players (11,538) were from cold weather areas, while 35.5% (6359) of all players were from warm weather areas." Tommy John surgery has only been common in the last few decades. The percentage of major league players from warm weather states over the last two decades far exceeds the percentage in all of MLB history (population shift to SunBelt over the last 50 years, for one reason). What percentage of major-league pitchers, today (or, say, over the last 20 years), not all-time, are from warm-weather states? I would bet it is close to the percentage (56.3%) of TJ surgeries from warm-weather states.
I think that the damage done to the ligament is not new, these pitchers left the game because their elbow or shoulder just hurt too much to pitch, or they drank heavily or took drugs. One of my sons pitching is a former ML, Dennis Martinez, I am sure that you know who he is. He is a recovering alcoholic.
He also came from a warm weather place. TJS is pretty common for latin pitchers as well as warm weather US pitchers. It is also common in those that throw well into the 90's.
Also keep in mind, that all boys/men develop differently, and many of these young players with TJs arent developed to their fullest but they are throwing bullets and often over used, they go from the mound to the infield or catch in one game because they are so good. Thats where mom and dad need to step in. But many of those same mom and dads want their son in every game because well, he is just that good the team cant live without him!
My neighbors brother is a pretty famous guy who never played professional MLB ball but played proball in PR with many guys you have heard of.
Pretty interesting stuff, and I am sure it is the truth.
Thats why you dont play year round bb until you have to, but as PG states for some the risk is often worth the reward!