Since the majority of colleges are FAFSA only, the bio non-custodial parent IS out of the loop for the majority of college students, whether the custodial parent has remarried or not.
But the colleges aren’t the only ones being unfair to the single parent. The IRS is in on it too. The AOTC cuts off at $80-90k of adjusted gross income for single tax filers while married couples go to $160-180k, even if all that income is earned by one parent. A single parent can have 5 kids in college at the same time and get $0 in AOTC if the income is $90k, while a married couple can have 1 in college and get the full AOTC at $160k.
But it is what it is. If the stepparent’s income makes a CSS school unaffordable, that’s how it is. Many students can’t go to one school or another because they are unaffordable and thus have to search for merit, a cheaper school, a tuition reciprocity program or a money tree.