Reply #3: I speculated on this in the earlier thread [View All]

It's no accident that there're so many foul balls on 3-2 pitches, particularly by the contact hitters in the 1-3 spots. Hitters don't want to take a borderline pitch on 3-2 because it might catch a corner. OTOH, they don't want to try to drive a pitch that isn't in their zone. So, especially on 3-2, contact hitters will shorten their swings and intentionally foul off a pitch.

I'm guessing — just guessing, mind you — that this rule exists so as not to penalize these guys for being particular.

BTW — in the old, old days, like the 1870s, there was a rule by which a foul ball caught on the first bounce was an out. It was called a "fair foul" — fair to be caught, one supposes.