That’s a really big part of it. There was a time when the Gary schools were formidable football programs. Same with Hammond. The decline in the steel industry over the last 50 yrs., with the corresponding negative effect on steel support industries, resulted in huge population declines and population shifts in urban NWI.
Changing demographics is also a big part of it. The Hispanic population has increased significantly. But, as @Muda69 has pointed out many times, Hispanic athletes tend to gravitate toward sports other than football.
To me, the mystery is whether the population boom south of US 30 is going to translate into athletic success. St. John, Dyer, Crown Point, Cedar Lake, all are experiencing housing booms, many of which are move-ins fleeing the People’s Republic of Chicagoland. Schools like Crown Point, Lake Central, Hanover Central, Lowell, and of course, Andrean, should benefit. Their potential path is similar to places like Center Grove and Westfield. Notice I said “potential.”