There are several possible reasons: if your dough is too cold, the cookies won't spread as much in the oven. If you chilled dough overnight, try setting it out at room temperature 20-30 minutes before rolling your dough. If the oven is too hot, that can also reduce cookie spread because the outside will set before it has time to spread. Lower temperatures are generally better when it comes to chocolate crinkle cookies to give the dough time to spread. You may also want to check your flour measurements--if you've added too much flour, the dough consistency can be extra thick and won't spread as well.