If the stats are to be believed:
-In 2008
18 pitchers in the league could throw over 100 mph and through the whole season they combined threw 196 pitches over 100+ mph
-In 2017
40 pitchers in the league could throw over 100 mph and through the whole season combined for 1,017 pitches over 100+ mph.
HGH comes to mind but they're clearly doping and getting away with it. What do you suppose they're using?
I think its just more people training for it from an earlier age. When Nolan Ryan started pitching, a 100mph pitch was unheard of. You might as well have been talking about a 4 minute mile.