The concern, "we had to buy a million hard drives to store users' photos," ends up being fairly weighty. At the very least YouTube itself is an advertising plat

The concern, "we had to buy a million hard drives to store users' photos," ends up being fairly weighty. At the very least YouTube itself is an advertising platform... people buy ads on YouTube and those ads pay for the massive computing and storage running it. People don't buy ads to put in your personal photos and having a bigger training set than the next guy isn't enough of an advantage to pay for all your disks. Cloud photos may be smaller than YouTube but it's not small enough to "fall in the cracks" and get funded with spare capacity from running other "real" services, it's undoubtedly got real, proper funding which is justified because of how it positions Android in relation to iPhone, and how it positions the Google ecosystem within Android. In other words, Google wants Android phones to use the Play Store, and free storage on Google Photos is part of the carrot.