Yes, people in the US make more money, on average, than the average Ghanaian, but the relative incomes of a family are just as disparate as those of Ghanaians. If someone in the US gets a better job, the whole family doesn't suddenly also get better jobs.
This is why the kinship system is so economically counterproductive: The collective expectation effectively levels everyone down; any individual who begins to accumulate wealth faces pressure to redistribute it across the group. Nobody can grow their fortune, because that requires both having some fortune initially and being able to make investments that compound it. If the kinship group makes sure your fortune can't increase, any compounding you manage to do doesn't matter, because the initial capital always stays small.