It is life's experiences which contribute to an artists form. It isn't the fans or the audience or the marketplace. The fact that the market chooses to favor one style of music over the other isn't a reflection of the artist's style or values. Its just a natural phenominea that the market rules, not the artist. Not the individual.
Artists have many reasons for moving away from the core of the bluegrass sound.
It is true that many want fame and fortune. Others just want to achieve a new level of expression. Others may just want a change. While we are clearly aware of those who choose the country route, others have also gone on to folk and others into other styles. The artists are growing as does a child.