Where are people going if not staying with him? Only a few options out there. A few teams are only 2-3 really good players away from being really good? Realistically options are only going to Janelli, Lomo or TGs. Maybe jesters or Legacy??? Unless they want to drive and play for Grizzles or prime time!!
There are a few reasons and they might be good enough or right for some people. The YJ name has meaning. Like it, love it or detest it, it's still true. CR has the best connections in the business, the brand draws talent and talent draws college commitments. Some other clubs make blips on the radar depending on the grade but YJ is the Queen Bee of LI Lax.
Second, JS is a good coach. Any kid who plays for him learns a lot as long as you're in the top half of the roster he deems worth speaking to, or your daughter has really good ears when the top half is being taught. Either way, he does have a lot to offer if you're willing to overlook the downsides.
Lastly, there are the fanboy/girls "My daughter plays for YJ Spallina" - does she? Does she play? "Uhhhh, well, ... she's on the team ..."
These reasons are enough for some parents to hold their nose and deal, or stink up ad nauseam. Mostly the latter.