You are wrong. It can still be end-to-end encrypted using a password. Android backups are end-to-end encrypted (iPhone backups too but only if you enable the optional "Advanced Data Protection" feature) using your phone unlock code as a password. The phone unlock code is never sent to Google/Apple, it is only processed locally on your phone.
Your phone unlock code is typically not complex enough to withstand brute force attacks, so brute force attack resistance is added using an HSM in the datacenter (just as brute forcing the code locally is prevented using an HSM in the phone). A similar technique is also used by Signal, you can read about it here: https://blog.cryptographyengineering.com/2020/07/10/a-few-th...
Your phone unlock code is typically not complex enough to withstand brute force attacks, so brute force attack resistance is added using an HSM in the datacenter (just as brute forcing the code locally is prevented using an HSM in the phone). A similar technique is also used by Signal, you can read about it here: https://blog.cryptographyengineering.com/2020/07/10/a-few-th...