Baseball isn't a static game. Instead, it has changed over the years. This change has been driven by innovations in pitching, including the development of new pitches, as well as the evolution of the gear that umpires wear.
One thing that has changed is the strike zone.
Today's strike zone is significantly lower than the strike zone of 50 to 70 years ago.
If you look at clips of hitters from the 30s and 40s, you will see that they tended to set up much higher and less crouched with significant space between their thighs and their calves. If pitchers missed, they tended to miss up in the strike zone. That allowed hitters to use swings that were more level to the ground.
Now, catchers set up in low crouches, with their thighs resting on their calves. If pitchers miss, they tend to miss down in the strike zone. That has had a number of effects, including forcing hitters to Tilt more.