Because Tom Cruise is weird.
During an interview with All Headline News, he explained, “Katie is a young girl’s name. Her name is Kate now – she’s a child-bearing woman.” At the time, it was also reported that Holmes had agreed upon the name change “after discussing it with Tom” and as a result “all friends and family now call her Kate.”
Except none of them did, so that didn’t really pan out.
You know who else pulled this kind of thing? Napoleon. For real! When he married Empress Josephine – nee Marie Josèphe Rose Tascher de La Pagerie – everyone called her Rose. And Napoleon decided he wanted to call her by a name no one had ever called her before. So her just told her name was now Josephine. And her husband had just been guillotined, like, a week before that. That seems like it must have been a very uncomfortably tumultuous period in Josephine’s life.
Also, much like Tom Cruise, Napoleon was very short.
Good talk, everybody.
(Really, would you let someone call you by a diferent name/nickname? Sometimes it’s okay to change for other people! Sometimes it’s sort of awkward, though, like if you are famous and everyone in the world knows you by the name “Katie”.)