Because too many people are now taking early retirement without being prompted by the physically-taxing nature of their job. With this in mind, the government has already voiced its desire to partly fund the state old age pension by taxing older people’s incomes.
In itself, the idea of funding state pensions from public resources seems a good idea: older people would then help carry the collective burden of population ageing. All other things being equal, it would allow for a reduction in general tax rates, and it is also expected to boost total labour participation.