Utilities
Think about the pandemic period when you had to work from home. You must know utility bills piled up and the reason for that is you were home almost all the time.
Well, this also applies to retirees: being home more often means using different appliances, watching more television, maintaining a living temperature all the time and so on. This translates to higher costs for utility bills. Simple as that.
As a side note, maintaining the right temperature in older homes is more expensive. Construction techniques have changed and insulation has improved so a modern house is cheaper in terms of heating and cooling.
