It isn’t odd that there are a lot of things called “rosebud,” if you just think about it for a minute. Rosebuds are pretty common and pretty nice. That Kane’s sled was named “rosebud” was just an ordinary bit of prettiness. It could have been “Swan” or “Pretty Boy.” The symbolism that was intrinsic to the name was in its context, not its associations. Some other things called “rosebud” include: a hockey team, a Sioux Indian tribe, an Italian restaurant in Chicago, a county in Montana and a guitar belonging to Jerry Garcia.
Only the latter has any possible connection to Orson Welles’ invention of Kane’s childhood memory, and that, speculative. Someone speculates Garcia could have renamed the guitar — originally called “saint” by the luthier who made it — because he was “into film.” The same source notes also the rose in the teeth of that famous Grateful Dead icon, the skeleton. That seems a bit more likely to me, but who knows?
The Sioux tribe had its name a long time before any of these other things got named and apparently the hockey team has been around for a while too.
Personally, I’m very sympathetic toward the idea of naming a diner, “rosebud.” Rosebuds are so petite, diners so very not. Although some seem more so than others. As for counties and restaurants, why not?
The gist of all this? It’s not so remarkable that good endeavors get to be called rosebuds. The word, after all, has had plenty of practice.