Devil's advocate:
And nor should they. Governments have to fill their coffers from somewhere.
Tempting to focus solely on the financials but there are at least two other legs to the stool.
Governments also have to reduce our carbon emissions, and improve public health. Don't blame them for keeping the tax % the same (and thereby increasing their income) as it might dissuade us from burning as much diesel. About half the average UK households emissions are from transport, including about 10% aviation, so diesel price rises may have positive environmental and social impacts.