Why can't the masses be kept in poverty by restricting the output of goods?

Are you referring to the book 1984?

yes

The Proles were kept in poverty, the state didn't need to limit goods. Goods were found on the black market. The Inner party kept the Proles in in a state of perpetual ignorance: that is what kept them in poverty.

Can you explain it to someone who never read the book? Like do you know where I can find that answer?