Some, not all people, when given all day to work on something, whatever it is, tend to not be productive with their time. They don’t feel the pressure, they take it easy, they tell themselves they’ll do more later, etc.
Someone who wants to learn but had limited time, which is usually the case for those who leave yeshiva, if they’re serious about it will maximize their time due to the pressure.
Similar to how someone with a lot of money will spend more casually than someone with limited funds. It’s human psychology.