Odds of Getting In
As with your clients and their careers, there's a lot of luck involved in becoming a talent agent. You can absolutely improve your chances by pounding the pavement, maintaining strong relationships with executives and performers alike, and exhibiting a willingness to bow a little lower before those who can better your position—but sometimes it's just luck of the draw.
Have you aligned yourself with enough actors who got lucky themselves? Hopefully that whole "screening process" thing you're doing is actually working.