In Maryland you have 4-5 MIAA schools that are loaded up and concentrated with the top kids in the Baltimore area. In the DMV you again have 4-5 either IAC or WCAC teams that are a concentrated pool of top local kids. After that those leagues have an ugly bottom half and the public school leagues are terrible.
People can post all day long that "only" a few publics in LI can compete at the high MIAA level. The point is there are 30+ townships that have very good public school teams. Maryland and DMV taken together don't have 5. I also think that the top DMV and MIAA teams have started to lose fairly consistently to the Philly preps coming down to play. Maryland lacrosse has been in decline for the last 5-8 years. I think a lot of that has to do with the growth of the game lifting the competition, but also just that the clubs in Maryland do a lousy job developing talent relative to LI and Philly.