Part is availability. Youth injury rates are probably really up some maybe partly due to year round throwing and other stuff but I guess TJ wasn't really that available for the public 20 years ago and many 16 year olds would just retire from baseball or become a position player only if they blew out their arm.
Now there is the option to continue. Maybe some are reckless pushing it too hard knowing there is a chance but really pitchers always had arm problems.