WEIRD people set standard
What we know about human behaviour has a strong cultural bias. Henrich et al. coined the term WEIRD to describe the group of people most likely to be studied by psychologists - Westernised, Educated people from Industrialised, Rich Democracies.
If the norm or standard for a particular behaviour is set by
WEIRD people, then the behaviour of people from non-Western, less educated, agricultural and poorer cultures are inevitably seen as 'abnormal', 'inferior' or 'unusual'.