Always_Ask_Questions,
“Others wear whatever was worn by reasonable people at their time – jackets, hats or caps, depending on time & place.”
Fedoras, dress shirts, and suit jackets were all garments commonly worn by the general American population through at least the 1950s. The American yeshiva communities have subsequently settled on a particular subset of these (formerly) common garments: white shirt, black pants, black suit jackets, and black fedoras. If rabbonim are wearing black fedoras and short jackets that are indistinguishable from what the yeshivish rank-and-file wear, then it is those rabbonim who adjusted their style of dress. And it is the uninformed assumption of those unfamiliar with the yeshiva community that black jackets and hats automatically equal clergyman.