It has zero account for quality or outcomes.
It doesn’t care if you have access to healthy foods, it just cares how much would X calories costs, it doesn’t care what is the quality of the housing stock or the outcomes of your healthcare system.
You can very much have a situation where your economy shrinks, the quality of life tanks and your GDP PPP stays the same or grows, communism is rather good example of just how a situation can be where things are on paper very cheap from food to infrastructure mega projects and where housing is free but no one would claim that life in 1970’s Soviet Union was particularly great.
In 1990 the USSR had the 2nd highest GDP PPP in the world, if you honestly think that it was a good place to live I’ll build you a time machine myself.