What’s the motivation for app makers to completely opt out?

I understand that some data is considered cached and shouldn’t be backed up. But Android already allows that.

> Auto Backup excludes files in directories returned by getCacheDir(), getCodeCacheDir(), and getNoBackupFilesDir(). The files saved in these locations are needed only temporarily and are intentionally excluded from backup operations.

Overall though, this has been a solved problem since 2010 on iOS. True you only get 5GB of iCloud storage by default. But you can pay for more or use iTunes for local backup

Basically, opting out is the most reliable way to not accidentally give Google full access to private use data because backups are stored in their cloud by default.

My understanding is that this was the same for Apple until they added e2e encrypted backups, but Apple users seem much less sensitive to privacy violations done by Apple (which is probably reasonable given that Apple is not as focused on profiting off of data)