Most likely it's due to the hilariously stupendous amount that the state pension is costing the Govt. When it came about people only lived for around 10 years after retirment age. That doesn't hold true anymore. It needs to be aboloshed for new births and every child given £5k to be put in a SIPP to be redeemed at a pensionable age. However no party in power is ever going to do that so it's going to continue to cost a fortune especially as people live longer.
They are stepping towards that with auto enrollment already.
I entirely expect the state pension to be means tested by the time I reach retirement age. Those with a full LTA will get zilch from the state.