#3 Family adheres to a particular Chassidus and boy will attend an affiliated Yeshiva
See my response to iacisrmma regarding RSA.
#6 Finances It may not be affordable for the boy or family for him to be at BMG
They accept Pell grants.
#7 Boy attended a feeder High School for a yeshiva
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This yeshivas are generally for younger bochurim than those who attend BMG. That being said, there are some yeshivos which do have a program for bochurim returning from Eretz Yisroel.
Not accepted is a reason, perhaps wanting to stay closer to home occurs, but I think the number 1 reason would be wanting a smaller yeshiva, with athe opportunity to gain a kesher with the rosh hayeshiva.