Imagine two people. One of them is named Betsy Kaplan, the other, Betsy F.P.R. Academic studies suggest people, on average, would infer a higher intellectual capacity for Betsy F.P.R. Kaplan and be more likely to admire her and think she made more money than plain old Betsy Kaplan. A middle initial, says the scholarly literature, is basically a free ticket to higher status.
Which makes it odd that each successive generation is less likely, overall, to use them.