There are a few reasons your bone broth didn't gel, but the base reason is that there's not enough collagen in the broth. Collagen is the substance that causes gelling and can be found in the gristly, cartilaginous bits and joints of bones. To maximize extraction, you need to add an acid to help break down the bones, simmer for longer, and make sure there are more of collagen-rich bits like necks, wing tips, skin with the fat rendered out and, you guessed it, feet.