Because an unenforceable right is only a promise. The chapter says exactly this about the right to constitutional remedies: it “ensures that these rights are not just promises on paper but can actually be protected and enforced.”
Follow the chain the chapter builds:
These rights can be enforced by law — if they are violated, people can approach the courts for justice.
Article 32 is the door to that court: the right to approach courts to protect Fundamental Rights.
Remove Article 32 and the other five categories become advice, not law.
You can see the same logic in the chapter’s own story, at a much smaller scale. Meena was kept out of the debate, Ravi out of the library stall, Gaganjit out of the exhibition hall. Their teacher’s answer was not sympathy but a route: “If any of these rights are denied, citizens have the right to approach the courts for justice.” Once the children took the matter to the fair organisers, the changes were actually made — a right that has somewhere to go gets results.