Hamas switched from smartphones, with encrypted messengers to pagers, a communication device with encryption so weak it may as well not be there. Criminals get caught because they used plain phone calls and texts _all the time_. Hell, child abusers are regularly reported to the police because someone saw a suspicious picture on their phone when scrolling through the gallery. Crime and an understanding of cybersecurity don't necessarily overlap.
I agree that cloud services cannot be trusted to do encryption within their clients, but on platforms like iOS it's difficult to do automated backups using independent encryption. It's also quite difficult not to accidentally enable backups to these services because the setup flow for every phone guides you to hitting the "upload everything I do to Apple/Google".
To Apple's credit, while they normally store a copy of the encryption key, making most cloud encryption entirely useless, they do offer setting a custom key at least. GDrive and OneDrive sure don't.