It's far more complicated than that. How do you measure inflation across the world of disparate currencies and circumstances across a century? How do you measure it in hostile zones? Some warlord/dictator isn't going to report how much of their population is in poverty.
The error margins would be massive even if you could.
Then there's the complication of poverty vs extreme poverty.
Ultimately what we want to measure isn't 'do you have enough money' but rather 'do you satisfy your maslows heirachy of needs' or rather really how much?
If you look at a tribe, their physiological needs are met, their security needs are met, they most likely have friends and good social order, they very likely have a sense of accomplishment. So what's the problem?
Flipside, we in the rich world have created multiple planet wide problems and what if those tribe people are who have the solution? We want to get them connect to the internet as soon as possible.