Because the release point of a baseball pitcher does not occur near the uniform. However baseball does have rules about what can be in the hitter’s line of sight behind the pitcher.
And that was specifically mentioned in the release from USA softball.Softball was played with white ball for years. I still have some.
OP stated it was the uniform color that he was referring to.I am looking at the face-mask and he round shape of chin area. Perhaps that is what the OP is questioning.