"Sassoon's analysis of how we're taught to hold pens makes a much stronger case for the role of the ballpoint in the decline of cursive. She explains that the type of pen grip taught in contemporary grade school is the same grip that’s been used for generations, long before everyone wrote with ballpoints. However, writing with ballpoints and other modern pens requires that they be placed at a greater, more upright angle to the paper—a position that’s generally uncomfortable with a traditional pen hold. Even before computer keyboards turned so many people into carpal-tunnel sufferers, the ballpoint pen was already straining hands and wrists."
Josh Giesbrecht in a 2015 Atlantic article argues that the rise of ballpoint pens made handwriting more difficult.