If Illinois used a more conservative actuarial method to estimate liabilities, amortized over no more than 30 years (or a shorter period, as is used in many states that want to get a handle on their pension liabilities) and used a more realistic return assumption for TRS, those pension contributions would be rising even faster.
Banks are behaving on the assumption that a further 20% fall in the price of UK homes is a realistic probability, and are protecting themselves against that eventuality.