So what exactly is driving the developers to keep going?

[Raikai]

So what exactly is driving the developers to keep going?

Its their Job.
They are Game Devs, Creative Business Unit III. (CBU3)
They are given a Job, and they do it.

I think the OP asked more on a personal level - which is not anyone but the person themselves that can answer.

Even if it's my bread maker, I honestly don't think I could keep over a decade following the same modus operandi with my work. Gladly I don't have to and I'm able to reinvent myself every 2 years or so - I work in the art industry. But I personally know people who are spanning 20+ years of career by doing the same thing. I guess it depends on the person.