You’re just yappingThe problem word here "mainstream"
Pop & Rap are the only genres making up mainstream, with rap being practically pop in & of itself. What's sold in the mainstream is mainly image & stardom , not music. so of course that lends itself to young people.
Taking mainstream out of it Jazz is jazz regardless of age, classic rockers are doing much better than any current day bands etc.
Rock is a dead genre. Jazz has always been irrelevant
Music is sold and the youth decides what’s popular