Convenience, speed, and technical difficulty (for the typical person, not HN reader). Definitely, I've faced this problem. My photo and video library on Google Photos is now much larger than the free space I have on any device. The hassle of downloading in chunks, just to re-upload (and heaven help anyone on an ISP with data caps) is huge. It's also probably very slow - consider the bandwidth between an Apple and a Google server - most likely in the 10Gbps range? Compare that with an average person doing 50Mbps down and then 8Mbps up. For a 500GB library that takes _hours_.