This is because 98% of people with hearing loss in poorer countries have no treatment for their hearing loss. 100% of them are less educated and in lower paid jobs
Hearing loss in children is an invisible disability and easily confused with learning difficulties or lower IQ. Thats why affordable universal screening is so important.
In many countries children with hearing loss are not accepted in schools or kept at home by their parents, dismissed as unteachable and destined to remain illiterate.