It's a price-segmentation system. It's not about fair. They have to target limited grants without much information to get the best set of students they can (plus probably keep some politicians happy about their demographics).
Household income of parents is obviously a bit of weird proxy for an almost-adult child. But, I bet it works quite well at finding academically inclined people who assumed they couldn't afford X University and persuading them that they can.
The alternative would probably be something like requiring all parents to buy "education insurance" for their children, which turns into a lump sum at 18, and then giving people with lower incomes a discount on that insurance. (This is a terrible idea, don't do it. Make education cheap or free instead.)
I also asked a specific question, which you completely skipped, while doubling down on a fairness argument that this thread wasn't even about. You act knowledgeable in the matter and then aren't able to dive in, only defend your position. Its fine to say "I don't know", but right now what are you doing?
Were you saying that Harvard's "affordability" was anywhere close to the $3,000 tuition / semester I ended up paying? And that's because Harvard routinely makes up any number based on a variety of financial variables (which aren't as simple as "income") and ultimately feelings?