it may be the result of evolution in an artists music. Like Darwin said, one needs adapt to its environment in order to survive and prosper. Those select few that can reconize what it takes to sell hit records, will ultimatley last the longest. Those who have a variety of music like aerosmith and the rolling stones still have a distinguished style that their fans can relate to. In order to avoid being a one-hit wonder, ones music needs some meaning to their songs. Sure a catchy hook like soulja boy can get you instant fame but you need to follow up with a more meaningful songs than batman and spiderman.
Somethings you just need to stick with what you got because your style may just have that special something that your fans can relate to. Darwin also said that the strongest will survive because that pocess a distinct trait which will aid them in their survival. Artist like Elton john and micheal Jackson may branch out into different genres but they voice and characteristic style will forever be reconized by their fans.