I would imagine depression and life problems play a major role here. It's hindered me many times.
But I'm currently homeless and I'm still working my arse off, sitting at my local bar with my laptop and writing and drawing like there's no tomorrow. For me, it's the only thing that keeps me going.
But for others... it's harder to keep up with when life problems pummel you, bills to pay, loved ones enduring strife, and personal depression, which is something common among most authors and/or artists. Creative folks often feel discouraged from trying, especially when they fail to garner their desired audience or when they see someone else gain a ridiculous amount of success.
Then, there are critics who don't try to be constructive. Criticism is very necessary, but some folks purposefully try to rip down your work and make you feel like a damn fool for even trying, and this is mental kryptonite for any creators who haven't yet developed the thick skin they need for the job.