Me personally it's money, sad, but true. I am a single guy, making uh simple 2D games as of now, and will make more and more till I am confident enough to dabble into 3D.
I am not a creative person, I have ADHD and don't focus on a single task often, sometimes my attention span is no longer than 10 seconds if I find a particular task too difficult.
I have literally no ideas about what games to make, so I just focus on making a map and character appear as well as accept KB input.
As for the creative side, I cannot draw, but even if I could, the image of what to draw is always blank, nothing is there. So yeah, I can't draw because I don't know what to draw, but then if I did, I can barely draw a circle(both on a computer and in real life).
And then there's money, there is no guarantee I will survive 2D to even begin with 3D, but I do hope I have a one in a few thousand chance like Notch to create some fun game. More specifically, money, because I lost 2.15 Bitcoins to gambling, which at (variable)current price of $118 is 253 dollars and will likely go up.