The final nail in the coffin was in 2014, when iOS 8 got serious about the standard Photos app. It got proper editing features, print products, smart search, and photo extensions.
At the same time, a check was hard-coded into the system to prevent iPhoto from launching, presenting this alert instead:
This entire thread has made us reflect on the work we do. It’s extremely ephemeral. It’s an art form where you could spend two and a half years crafting a beautiful product, only to have it killed for business reasons.