A few things going on:
1) KAH has never been persuaded by star ratings. She and Scott have an amazing eye for talent, and recruit players who fit with their system. They rarely have a top-rated recruiting class.
2) Most lax players are from the East Coast, so NU is farther from home.
3) KAH and Scott have said that part of their success is that players who come to Northwestern come because they want to work hard and win Championships. The players just tend to be more driven. b/c if you want a lifestyle school, then Virginia, Duke, UNC, BC, Michigan, Penn, Princeton, etc. all offer a perceived better college experience. Those schools naturally attract players, regardless of who their coach is and how good the lax actually is.
4) With the new House vs NCAA settlement, Clemson, Florida and some other public schools are now offering full scholarships to all players. This is hurting private schools where tuition is higher, so it costs the Athletic Department more to give full scholarships.
All that said, this year's recruiting class doesn't look formidable on paper. But we'll see how it plays out, since they won't step foot on campus for 2 years!