Unlike Bishop Amat, Mater Del and Servite and maybe a couple others the majority of adults who travel to games is limited to the parents, adult siblings, aunts, uncles and grandparents of the players, band members (if the band even travels) or cheer squad, plus some administrators, a handful of alums and the coaches wives.
The idea you put forth - that a parent of a kid not part of the program, cheer squad or band would want to spend a Friday night at a high school football game simply because they dropped them off at the venue - is comical.
At places like Bishop Amat where the cultural ties between the school and community (beyond just the city of La Puente and the local parishes but the entire San gabriel Valley) run deep you see not just adult alumni but parents of non-athletes and regular everyday people from The SGV traveling to road games. At MD you have a huge multigenerational alumni base that can - and will - arrange their schedules around Monarch football and basketball. That type of thought process doesn't exist 99% of schools and certainly not at places like SM or JSerra.
Does a parent of a volleyball player or thespian occasionally attend a HOME football game now and then? Sure, however, in south Orange County getting that parent to travel even 5 more miles to a road game and sacrificing a date night with their spouse is pretty much unheard of. This is Why SM has a large contingent of rooter busses - to get kids of disinterested/ non-vested parents to the games.
South Orange County adults simply have better things to do.