The UK State Pension is payable worldwide and is uprated abroad where there is a legal requirement to do so. In most overseas countries, however, there is no agreement with the UK for securing the social security rights of people moving between the two countries. As a result, pensioners who move to these countries still receive the State Pension but do not have their payments uprated as UK residents do. The Department for Work and Pensions endeavours to make this clear to those thinking of moving abroad and publishes guidance on its website.
I appreciate this is not what you wanted to hear, but I hope this helps explain why the situation is as it is.
Although the current policy on the State Pension overseas is the long-standing and unchanged position of successive Governments, I am aware of the report that the APPG on Frozen British Pensions has produced and will make sure to read its findings and recommendations.