There's a bizarre obsession that musicians have with pushing the envelope. Once any major success has been achieved it becomes a point of principle to work out exactly what got them into that position and, no matter what it was, stop relying on it in all future releases. Finding the "new sound" is usually way more important than remembering why people bought the old one.
But, as decisions in the music industry go, this one rarely makes any actual sense. Experiments in new directions and personas are fraught with disaster and, even if you do manage to pull it off, you run the risk of alienating the fanbase because "wow they really suck now, I guess". Your comfort zone might be boring, but nobody goes broke sitting in it.
However, some artists concoct such a bizarre trademark that it sneaks its way into all their releases without them even realizing it. A dirty habit, a creative crutch, sometimes even just a nervous tick, the human brain's a weird machine made even weirder when it's trying to maintain a music empire.