Human motivation is complicated. Chances are that ones relationship to some kind of labour is mixed with both intrinsic and extrinsic motivations: implementing the back end might be fun for you, while the front end is tedious, or vice versa. Or maybe it was only fun to make 90% of the features, while polishing those features and delivering the last 10% is a lot of tedium. Things like this might help to make some open source products more well-rounded.