Large portions of the worlds children grow up with barely primary school level education and an economic reality that requires them to go into work as soon as possible.

When would they have the time and money to set aside to get deep into a subject that most of them do not have the academic background to see the value of?

Yes, everyone could learn mathematics. Just like everyone could get rich and go into space. It's just that for a huge proportion of people the pre-requisites are not there.