Good entrance music: it's what separates the top guys from the jobbers. It can create legends, or it can turn talents into laughing stocks.
Of course, whether or not entrance music is "good" depends on a few factors. The first is longevity; the longer somebody uses a song as their theme music, the more fondly people will remember it, no matter how "good" it actually was. Objectively, "Sexy Boy" is kind of a s**t song, isn't it?
No matter who the composer is, they must get frustrated whenever one of their compositions is swiftly replaced or re-worked. It not only means that they have to compose more music, but it also means that their efforts were for naught. And God forbid they compose something for somebody, only to have them get released soon after. Might as well throw your composition in the trash at that point.
This is not to say that the entrance themes that don't last, for whatever reason, are all bad. As a matter of fact, many of these short-lived themes are what some might call "hidden gems". Let's have a listen to a few...