High school bball in Chicago has changed (a lot) over the last 25+ years. DePaul and Illinois (plus a few other Big Ten schools - IU, Michigan) used to get all of the kids that played in the public high schools on the south side. And DePaul had access to the Catholic high schools in the area that sent their boys to a Catholic university.
That’s all dried up. The South side has become a gang-infested wasteland. And all of the promising prospects go to prep schools around the country. The northern suburb kids go to Duke.
Chicago ain’t the hotbed anymore
Matas Buzelis left but that's all I know about. There certainly isn't any exodus of Chicagoland talent to New England Prep or any other Prep around the country.
There isn't the Derrick Rose, Ronnie Fields, Kevin Garnett, Benji Wilson, Jahlil Okafor, Anthony Davis at the moment but there's still a ton of talent in the area. The next biggest/star names are most likely going to be the trio of freshmen point guards- Davion Thompson, Jaxson Davis, and Devin Cleveland. They all already have Illinois offers and are doing things not many or no local freshmen have ever done.
None of what you're talking about has dried up, there seems to have been like a three to five year blip where they're not kicking out the extreme talent like usual but there's still the public school powers and Catholic school powers and still the awesome talents coming up...
The South Side has been a gang infested wasteland for decades and has been producing high D1 talent and NBA players for decades. Same goes for the West Side which is even more dangerous than the South Side.