Let me present to you the P.I.L.E.S. model of creative motivation.:

P - Pragmatic
I - Intrinsic
L - Learning
E - External
S - Self-concept

Like "look at these PILES of projects and the different textures they all have. Why do I currently feel motivated to do this one thing but not the others? Ahhhhhhhh!" [1/8]

Keep in mind that any one project (at least most healthy ones) tend to have multiple of these motivations.
Pragmatic motivation is wanting to make a thing because you want it to exist. You want to draw because you want to have the drawing and so on. You know something is pragmatically motivated if you'd be fine if someone else made it for you (for free, exactly the way you imagine it) [2/8]
Intrinsic motivation is the joy of the craft. I write because that's just the thing my brain does to keep itself sane. If you could simply make the thing and then destroy it without ever showing it to anyone, it's probably intrinsically motivated. This might sound like the most straightforwardly "pure" one, but intrinsic motivation alone rarely leads to great works. It doesn't encourage challenging yourself and it doesn't encourage actually finishing anything. [3/8]
Learning motivation is doing a thing because it's challenging, or to get better at the craft. Whenever you're doing something despite the product being unlikely to turn out the way you want it to, and despite the fact that the process is difficult and stressful, you are here. You're doing it to improve your future works and yourself.
Pretty much whenever you start out on a new skill, you will need a significant amount of L-motivation. [4/8]
External motivation is oft derided within artist circles, and it can be a poor engine due to how unreliable it is, but there's nothing wrong with a little praise. External validation can lead you to find new friends in your chosen discipline. Just be cautious with this one. Make sure you actually like the things you make as well. [5/8]
Self-concept motivation too can be perilous if it isn't supported by other types, but as a bonus it can be incredibly satisfying. "I want to be the sort of person who does this". It's not about external perception, but your own sense of who you are. Be your best self. [6/8]
I and L help you to start projects,
P, E and S help you to pull them through to the end
P, L and E help you improve
I and S help you to not be miserable as you do so.
Keep a balanced diet, make sure you don't deplete yourself, and create. [7/8]
As far as I know this system is an original, but if something similar already exists out there in the digital aether, I apologize for inadvertently plagiarizing it (also please tell me). [8/8]