What bands have done this to you? It’s not always the popularity that changes a band they naturally progress and change. A few bands I used to love are Muse, Linkin Park and Panic! at the Disco but they have progressed into bands that I don’t like as much now. Still talented people just changed for me and my likes.
On the other hand bands like Enter Shikari and Periphery who I also loved in their early days are changing but into something I like still. Progression is just a natural part of music.