A lot of the Beatles' songs -- particularly the early ones -- were written as throwaway pop tunes for a three-minute radio format. Given the context and intent, for the most part they are surprisingly good -- lyrically direct, musically engaging and interesting. But I don't think anyone expected that people would still be covering them, regularly, forty years later.

Often Lennon and McCartney would come up with a good verse or two, and then force themselves to come up with a bridge. Since they didn't want to end the song with the bridge, they would just repeat the first verse. Again, it was disposable pop, and as soon as they were done with one they moved on to the next. There are lots of examples of this on the first few albums.

As for jazz musicians, I think that "something new out of something old" approach is what I was talking about. The difference is that jazz musicians often hope to achieve that spontaneously through improvisation. But you can sometimes hear a more planned approach by jazz musicians in the initial statement of the theme; Coltrane's "My Favorite Things" is a good example of this (there are many others as well).