Am I supposed to believe that they've been selling cellphones for almost three years without putting their recruitment strategies toward their fulfillment chain?

Yes. People fuck up all the time. My employer has been in the eCommerce for almost 12 years and we still have feature launches that destroy our website. I'd say I work with some of the brightest people I've ever had the chance to work with, but we're still just human and we sometimes underestimate demand and over estimate our hardware. Just because Google is Google doesn't mean they are infallible, they are perhaps overly arrogant due to their culture.