When guys throw 100 mph, they don't need the assistance of a mound. Just something to talk about!
I'm sure there are longer, more detailed, and more thorough analyses than this little historical blurb, quoted below. https://bosoxinjection.com/2013/12/13/pitching-mound-history/
"Before the pitcher’s mound was introduced in 1893, there was a 4 foot wide by 5 1/2 foot long box on flat ground; the pitcher could put his back foot anywhere along the 4 foot back line of the box, which was 55 1/2 feet from home plate, to start his pitch.
In 1893, to create more offense, the box was replaced with a raised mound and a rubber slab 12 inches long and relocated further back to 60 1/2 feet from home plate. Pitches were required to be touching with their back foot and the rubber plate was 60 1/2 feet away from home plate.
The extra five feet was significant, as it cut down on the angle of the pitches and the league batting average spiked up 35 pts. in 1893 and another 29 pts. in 1894.
Until 1950, MLB only required that the height of the mound be no more than 15” above the baseline, but did not address a minimum height. This lack of interest in the state of the mound by MLB led to attempts to adjust the height from 0-15 inches to suit the style of individual home team pitchers, or work against the style of visiting pitchers. [After 1950, the mound was required to be 15 inches, no more, no less.]
The last time MLB made a major rule change for the Pitchers’ mound was 1969. In reaction to the complete dominance of pitching over hitting in 1968, MLB attempted to recalibrate the balance to favor the hitters by lowering the mound 5 inches to a height of 10” inches above baseline.
This was one change that was part of a general policy to make the game more exciting for fans by increasing the number of hits and runs scored,"