There are a large number of parents who aren't willing or able to support their children at Uni, despite their income. Some don't plan for it, some don't care, some prefer to spend their money in other ways, there are many, many reasons.
Not having had children myself, I don't know exactly what's taken into account when they look at the parents income - do they look at salary/ investments/ business income purely or disposable income?
If it's the former, that would be totally unfair as the parents could have many commitments such as other children, large mortgages, debts, dependent parents, large costs of commuting/working clothing or equipment etc. You see parents on here with high salaries but still struggling because they have to live near to (expensive housing) and commute into (expensive fares) London, they have SEN children, they have previous debts, one parent is paying towards child maintenance from a previous relationship etc.
Another thing that clearly hasn't been taken into consideration, which affects more middle earners than higher earners, is the massive increase in the cost of living over the last couple of years e.g. My income is around 25% more than it was 2 years ago. I was comfortable then, I'm struggling from pay day to pay day now with if anything fewer outgoings. And this isn't for big ticket or optional items, this is absolute necessities like food, transport and mortgage interest. Parental income cut off for university loans I'm pretty sure hasn't increased by anywhere near that amount or even to allow for the high inflation over the last 2 years, if at all.
Yes I do understand that some very high income families may well be doing well out of this, but this government seems to believe in punishing all for the transgressions of a small minority - listen to their rhetoric around benefits for the unemployed as an example, suggesting that all unemployed are that way by choice, or the policies around disability because a very small number of people take the piss.