Recasting tends to come as a result of money disputes, screen time, or any number of production-based disagreements. In the case of Claudia Wells, it wasn't hubris that opened the door for Elisabeth Shue to take on the part, but rather, her mother's declining health.
By the time the sequel came around, Wells' mother been diagnosed with cancer, and so Wells elected to pass on Back to the Future Part II, to take care of her ill parent. As she told People Magazine, "Life was very, very difficult and stressful. I just didn't have it in me to do anything but deal with the stress and the emotions that were going on as a result of my mom being in the process of dying. I just wasn't in a place to be able to think about my career or the film or anything other than what I was doing with my own life." Wells even retired from movies altogether for quite some time, not appearing in another film until 2008, for the independent project Still Waters Burn.
Despite Shue taking over the role for second and third Back to the Future films, Wells did get the chance to voice Jennifer, decades later, for Telltale's episodic Back to the Future video game, and later appeared in the short film Back to the 2015 Future. At the end of the day, she made the right call by choosing to provide for her sick mom instead of going off on another fictional time-travel adventure, and besides, while it might have taken longer than anticipated, she eventually got to return to the Back to the Future universe, so everything worked out for the best.
