Nowadays the junior idol sphere tends to be social media driven (twitter, etc), i'm not sure if there even is an "industry" anymore in the same since it meant in the 90s and 00s.

Many idol groups these days are more like a past-time extra curricular activity for the girls and typically their mothers are managers of their accounts/etc.
The groups are managed by other people who just coordinate events where girls sing and dance, and occasionally there are meet ups, where fans (usually adult men) will hang out at a park with the girls (and their mothers lurking near by) and chill and take stylish photos at parks or other fun locations, sometimes there is even BBQ, the photos are then posted to social media - typically twitter.

The age of photo books, and DVDs are long gone, and the "industry" is more like a pretend-talento for the girls, and its supported by your typical junior idol lolicon fans.