Canseco was sick of playing second fiddle to ARod, and saw his opening for another tit for tat go round.
This goes back years, Canseco always wanted to bang Madonna. They go out on a few dates, and he gets nothing. Fast fwd a few years and ARod is all over the place with her. Canseco drops the steroid accusation on him. Now ARod bangs his ex, and Canseco does this.