This is an extremely smart move by the fraternities. Obviously, when one is in the business of throwing house parties in an environment where it's really impossible to know if someone is of age, it is impossible to erase all potential liability. But the old system of supplying alcohol was extremely dangerous, both for fraternities and for the women who drank at the parties. Fraternities were exposed to liability not only for furnishing alcohol to minors, but also for any disastrous consequences of a party-goer drinking too much and being injured or dying from alcohol poisoning. The sorority women were at risk because they had no idea what they were really drinking (no, not date rape drugs, I spent 4 years at Truman and never saw anything close to that occur). 'Jungle juice' and similar drinks could be weak at one party and strong at another. A girl drinking a cup (or two, or five) would have no idea how drunk they really were....until they were throwing up on the front porch. Asking women to supply their own alcohol makes sure they know just exactly what they're drinking. Some might still drink to excess and wind up on the front porch, but at least she can't blame the fraternity.
As for minors being more likely to be caught with alcohol, this was occurring long before any mandate requiring people to bring their own booze. When people leave a party, they tend to take a beer with them. When people go to a friend's apartment, they tend to take some beer with them. Fraternities did not create this problem. MIPs will continue to be handed out not because the fraternity required people to bring their own alcohol, but because minors like to drink and are dumb enough to carry it around outside. All the fraternities have done is make sure that when the cops ask "where did you get this?" the person receiving the ticket can't say "XYZ fraternity." All of these things might not fully protect the fraternity system from liability, but it's the best option until they make the move to carding at the door, security at parties, and wristbands like a large big 12 or big 10 school.