Why jazz music has gone thru changes over its years of history?"?

This is a hard question. There are many reasons. One is that the taste of the public listening to Jazz has always changed. You can compare that with fashion. Besides that, Jazz used to be music to which people used to dance and this has changed latest when Bebop came out. Nobody would dance to the music of Bird or Miles...

It's called evolution. Everything must evolve to survive.

Musical tastes have changed drastically since the first Dixieland bands started and other musical genres influence changes in jazz. Pop music, rock and roll, blues, hip-hop, R&B and dance music have all influenced jazz in its evolution. The enduring quality of improvisation on the popular song or style is what has kept jazz alive for nearly 100 years.

the reason behind the Jazz Music.....(My own Personal opinion)

Jazz is not a genre,is a "tune"play it by a group of Musician that has "mastered at least one instrument" and has an outstanding knowledge of "how the music goes"
so to speak,any genre (pick a winner) has come from Jazz as Jazz has come from the Music Theory.

source:
I am a "weekends Wine'no piano BANGger", whom some times "plays piano" (for free) in a Jazz band at a Jazz Joint Bar in South Beach,Miami Beach.
( not a good credit ,isn't it?)
that is why I pay with American Express.

P.S.
I'd always think the Jazz Band likes me ,so much,because They don't have to pay me.(What Do You think?)

All music evolves, as tastes change and musicians create new ideas to go beyond what's been played before. I think john m is right, that jazz is not a genre, but rather a way of exploring music. Along the way, it has spawned various genres, such as swing, bebop, modal, fusion, etc.