Why commodore repeatedly shifted between rank and appointment

Why did the US Navy get rid of commodore as a rank?

There is no single established explanation here. The proposed reasons concern commodore's use as an appointment, attitudes to flag titles and the later development of a clearer admiral hierarchy.

Commodore has often functioned as a command appointment, which complicates its position in a permanent rank structure. One proposed explanation connects American resistance to naval flag titles with their perceived aristocratic character. A participant also repeats an explicitly anecdotal account from someone believed to have held US Navy flag rank: one-star officers disliked working alongside generals without being called admirals. The distinction between permanent rank and temporary appointment affected higher flag officers too; Husband Kimmel's return to rear admiral after Pearl Harbor is the example given. Large wartime commands could also leave officers doing jobs above their formal grade. Maintaining a large military after World War II is offered as a reason for developing a clearer hierarchy, including lower- and upper-half rear admirals.