Not having enough money to invest can limit their earning potential.
You probably (hopefully) did not experienced this, but not having enough money to buy food can limit their living potential. I say this as a disabled (I have multiple disabilities), former homeless person (I was homeless a few times), who lives on an income less than the local minimum wage.
Nowadays I am sometimes also on the edge of homelessnes. Sometimes I have to decide between paying bills/rent and buying food.