There are two reasons for tough roasts that cook in the crockpot. First, if you didn’t use a chuck roast or fattier cut of meat, there wasn’t enough marbling to create the fork-tender pull apart meat. The marbling is what melts away as it cooks to give you that juicy, delicious pot roast.u003cbr/u003eu003cbr/u003eThe second reason is the roast didn’t cook long enough. It takes time for the marbling to break down in the chuck roast. If your roast doesn’t easily fall apart or still seems tough, then give it more time in the crockpot pot. Depending on the size, you might need more or less cooking time.