The US is the least penetrated market when it comes to bikes. Uber changed the way people interact with taxis/cabs enough to make a cultural impact in many parts of the world, and it has the clout to do the same with bikes. I think it's a good diversification on their part, kind of insuring against the future where driverless cars won't necessarily become the de facto universal means of transit worldwide as the rest of America/SV seems to envision.