No matter how much I worry about the fact I never complete a project, 2 things bring me back and 2 things keep me going.
1: the #1 thing that brings me back to projects or start projects is interesting character and story ideas. Usually the issue is its a specific scene idea I have in mind but that seen is <1% of the game, so ends up not being worth it much
2: just cool game mechanic ideas and exploration. I consider myself more of a technical artist than an artist, and I'm way more of a programmer than an artist, so I'll often start an idea just to make a working prototype cuz its fun and cool, as Nicke mentioned.
what lets me put hours in? To be honest that's something I've been exploring, not just putting in more time, but learning about myself and my work habits and developing a workflow that encourages me to be able to put more time in. for example, I know there are certain things I don't like to do (enviorment art) that really slows down my productivity and breaks my pacing and kills a project. some things I can work around... and some things I can't (I hate enviorment art... but I'm slowly making my own art asset for this, hopefully to set up scenes in the future), but once I get in the groove 2 things keep me going
1: now that I've gotten more comfortable with my character art skills, I have no issue playing around with character just because the process is now fun now that I'm skill enough and have the resources I need (custom made sculpts) that its no longer 'effort' to make characters
2: I absolutely love programming. Again, its one of those things where I put a lot of time into it to develop the skill so that its no longer 'work' to make code, I can just have fun... that being said, anytime I have to learn how someone else code works (ie using a framework or API) I avoid it because learning is scary and hard and I'd rather just code things myself because that's just what I'm comfortable with.
but none of this actually equals results, just cool demo's. another thing that motivates me is aiming for a certain quality as my skill improves, which again prevents me from actually completing a project. but, started working with others just to try and learn, and its started to help with making more progress.