Re: belt drive, maybe?
I've IM'ed other members here myself asking this same question. For me it is about the look of the sheeve with the belt drive. Thus if you're wanting to make something that looks rather "retro" like a 1908 motorcycle which had pedals like a bicycle the project could accomplished.
I've viewed some sites where motorized bikes like we're building here were
dressed up to like some of those old early days motorcycles. The belt drive
would give it an authetic look.