The quality of music always depends on who you ask. That's about it really.
Anything else it's just business. Of course, it can get personal when one artist tries to use their influence to stop another artist from getting enough media attention, positive publicity from the press, showbiz bloggers, etc.
Furthermore, many radio personalities and DSP playlist curators are on major record label's payroll receiving them payola checks, therefore, the game is rigged and will always be rigged.