I think the reasons for the changes we are seeing now are twofold.
Firstly, the original business cases for these photo hosting sites are no longer valid. The original business case could not have foreseen the growth of phones with good cameras and social media. I know people who upload, and share, more than 10 photos everyday. Not just weddings, birthdays, seasonal festivities, and holidays; but meals, the dog doing something daft, and what Fred is doing lakeside. The bandwidth usage must be many times that planned for. Maybe a 100 times.
Secondly, I doubt any company wanted to be the first to bite the bullet, but once one made the move others soon followed.
Just some speculation.