[_-__---]

the evidence given in the article doesn't directly support this, but the author may have tried to get at the "[those that have] the necessary talent can learn any part of maths" statement you made. Without exposure to and engagement with a comprehensive education in mathematics (even just basic numeracy and arithmetic), it's incredibly difficult to teach oneself any given mathematical concept. Access to maths educational resources is ostensibly unrestricted, as (at least in the US) library cards are free of charge and the internet is readily accessible there; however, one can easily point at the many banes of lower-income households as immediate barriers to receiving any sort of education, either autodidactic in nature (i.e. sitting in a library with an geometry textbook) or through public schools.

It might be worth thinking in this "math for and from the elites" mindset when describing public aversion to the subject. Seeing it as beyond oneself or not relevant to one's life lends little towards anyone's desire to learn anything about it.

It's easy to say "why don't they just do it," with some diffuse definition of "they" in mind, but even the most basic things can be hard to get for the poor. A proper maths education is one of them, I think.