Why do people post links to shopping pages for books? Knowledge should not be held hostage behind a paywall. https://ia601805.us.archive.org/6/items/all-the-ma

Why do people post links to shopping pages for books? Knowledge should not be held hostage behind a paywall. https://ia601805.us.archive.org/6/items/all-the-mathematics-you-missed/all-the-mathematics-you-missed.pdf https://ia601805.us.archive.org/6/items/all-the-mathematics-...