The main reason it’s easier to be motivated in a project that is a “job” as opposed to a “hobby” is the job offers a more consistent secondary reinforcer. You’re “reward” for working hard is cash, and that cash in turn allows you to buy things that make you happy (thus, buying self satisfaction). Where as if it’s a hobby, your only reward is self satisfaction directly (a primary reinforcer). But, if that self satisfaction starts to dilute or completely dissipated, your drive to work will tend to evaporate.
