Portland, Oregon had a similar service in 90s. Painted yellow bicycles have been scattered along Downtown sidewalks free and available to anyone who needs one. Unfortunately, it was unsustainable due to theft and vandalism of the bicycles.
(I'm an American, and I wonder why we have so much petty crime here but not in, say, Tokyo.)
Additionally, Tokyo, as a populace, is much more collective and like-minded. A hive-mind, to be more blunt and offensive. Individual actions are taken in context of the whole rather than analyzed by itself. Thus, there is just about only bowing as a greeting there; whereas in the US, there's your choice of fist-bumps, high-fives, daps, pounds, pound-hugs, skins, or variations thereof. It's even distinctive by region or even state and city, or RACE.
So, because fuck it, that's why.