This is an interesting chicken-and-egg question we had not so long before - is it legislature or is it business that produces corruption? The answer is not black and white and depends on jurisdiction.
I fundraise for my kid's school. A local bank, ABC Savings, makes a considerable donation. There's no expectation that the school will pass a rule where we only accept students if their parents bank at ABC Savings. There's a difference between accepting campaign fundraising and quid pro quo.
In your own example - it's not like school will not accept somebody if they're not using ABC Savings. But they sure as hell will cater more to those who do, than to those who don't?