I don’t think there were nearly as many pitchers back then throwing mid-high 90s and I’d wager a lot less breaking pitches as well.
Ultimately, I think the human body was not designed to throw a baseball 100mph. You have to be a freak of nature to throw that hard, and an even bigger freak of nature to continue to throw that hard without serious damage to your arm/shoulder.
Edit: Going back to the Sano chat though, there is a really interesting story surrounding the Twins signing Sano a few years back. There is a documentary about it called Ballplayer:Pelotero. Here’s a quick synopsis:
“Sano was the big fish everyone wanted in 2009, but his asking price scared off a lot of teams. However, one team that was extremely interested was the Pittsburgh Pirates.
The Pirates knew they couldn’t give Sano the money he was asking for. Then all of a sudden there were reports that Sano lied about his age. The family felt this was an underhanded trick to scare away other teams and bring down the price so the Pirates and their scout Rene Gayo could sign him.
Sano’s mother even went as far as hiding a camera in her house before a meeting with Gayo. In the meeting, he told the family that “Unfortunately, this is the country of lies”. He basically told them he was Sano’s only way to get a visa to the US which he needed to be signed.
The MLB investigation was a peculiar one. It lasted quite a while and although he was eventually cleared as far as his identity, they said his age was undetermined. This meant they could not prove or disprove he was 16 at the time. But the most peculiar thing is when during a meeting with the MLB investigator (who is only there to investigate right?) told the family that if he signed with Pittsburgh the investigation would be over and there would be no suspension.
Sano didn’t sign with Pittsburgh. Late in 2009, he finally came to terms with the Minnesota Twins and received a $3.15 million signing bonus, which was a lower than the initial $4.5 million they thought he could get.”
Basically, it’s theorized that the Pirates leaked a false story about Sano’s age to decrease his value enough that they could sign him. Sano was partially vindicated and ended up signing with the Twins :).