Pull the age stats over the past decades for major league baseball fans and you'll see sportball has always been a boomer thing... they're "going elsewhere" as a euphemism for the cemetery.

Another thing is all sports over represent whites demographically, so if there's a big government immigration program to reduce the white demographic from 90% in the boom days to 60% now and ideally 0% in the distant future, then sports is just going away as an old white man thing. NBA and soccer are the only sports where the fans basically are not old white men. Another decade or two and it won't be a white country therefore not a sports bubble / sports fan country. Just simple demographics, non-whites don't do sports as much as whites.