I see two possible - and not mutually exclusive - explanations for this.
1 - They received a lot more applications, and thus the numbers really are higher in general
2- You have a significantly imbalanced set of scores. Let us presume you have a very high GPA and very low LSAT. Let us also presume that Notre-Dame puts a lot of value on factors other than GPA and LSAT. Chiashu runs a regression on only two parameters. Basically, it is saying the following:
everyone has a X% chance of getting in. Multiply the log of X by your LSAT and then your GPA. Exponent = chance of getting in.
If other factors are involved, the regression is not fitting very well. That is, it does not give very solid estimates. Consequently, a small change in the numbers of students being admitted will change the slope of the line which are implicit in the relationship above. If your scores are far from the mean scores, that might make a big change in your changes of getting in.
I realize this is not very clear. But just as an analogy, imagine that A- they are changing the direction of a road (the regression line) and B- your scores are 151 and 3.9. To reach your personal chance of getting in, follow the "LSAT" road for 151 units, and then, hop onto the GPA road for 3.9 units. If the roads changed direction - GPA moved towards the north and LSAT moved towards the south - from one year to another by a couple of degrees, people who have 162 and 3.5 did not get much of a change since they travel the same amount of time on the two roads. You, however, spend a lot more time on one of the roads. Your final destination is thus quite different.
Does this make any sense whatsoever to you?