Some of the many reasons:
* Different songs that touch every emotion and feeling that is possible.
* Sounds that have evolved and continue to get better as they continue to mature.
* Songs that have so many different themes and messages that are relevant.
* The span of ages - started as teens and are still rocking years later.
* Lyrics that means something back then, now, and will continue into the future.
...and so much more!
So, Bono (and Adam, Larry, the Edge), if you read this, I have full faith that your music will last at least 100 years! How else can you explain getting into the Rock and Roll Hall of Fame while at the top of your game? You guys are so good and to be together for over 25 years is so awesome, especially in this day and age. I mean look how few marriages (that only have to have 2 people to get along) last 25 years these days. All I ask is that you: "Keep it up!"
Bottom Line: I will never forget what you have done for me, and I will continue to share my love for your music with everyone I know... (Which is doing my part to make it last for the next 100 years!)