Why line art?
A) 3D modeling is too much work if I'm doing all the coding, music, and artwork - which seems like a healthy assumption if I intend to finish.
A2) 3D bores me. I must be getting old.
A3) Everyone's doing hyper-realism.
B) ANOTHER neo-retro fat pixel game? I don't think so.
C) Steve Yegge's 2nd to last blog post in which he points out the cartoonish cel-shaded graphics in Borderlands. Uhh, yeah, that's 3D, but it harkens back to traditional animation and comics. I'd never obsessed over that stuff at all, but it's a style I've long admired.
D) Around that same time, March 2012, I'd been fooling around with HTML5 enough to realize it was just about good enough to achieve that look in 2D games. Maybe not quite, but it got me experimenting.
E) I actually had the (2D) drafting chops to do the artwork.
F) I was blissfully unaware of "vector art" Flash games (which mostly use cheesy bitmap cutouts exported from Illustrator) and the fact that hardcore gamers kinda despise that whole genre
So it's just a challenging little niche I stumbled across... an interesting intersection of code and art.