Good point. I know they want to continue playing many of the traditional powers annually, so joining a light conference (and a small one with fewer scheduling commitments) still gives them the chance to do that while also having a relatively easy path to the NCAAs. I wasn't even aware that Marquette played lacrosse.
I believe they started last year or will start this year.
Regardless, the Big East probably needs 2-3 more associate lacrosse members to be eligible for an automatic berth. Perhaps that is why they are courting Hopkins and why they are interested in Richmond.