One has to remember that Notre Dame is first and foremost an academic institution with a limited number of spots in its undergraduate program.
It is my understanding that a comparably small number of students drop out … and the number of transfers in does not exceed the number of that drop out. In addition to that the transfer student is expected to have successfully completed the same required courses a student who attended ND straight from high school would have taken for the year he/she is transferring into.
Thus it is quite difficult to transfer into ND … probably much more so from a JC or a college that doesn't have or require students to take courses similar to what ND requires. It doesn't matter if they're athletes or non-athletes.
ND has had a few JC transfers in the past. But that has been the exception.